The effectiveness of interventions for reducing loneliness and improving perceived social support among people with mental health problems: A systematic review of recent literature

The effectiveness of interventions for reducing loneliness and improving perceived social support among people with mental health problems: A systematic review of recent literature | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article The effectiveness of interventions for reducing loneliness and improving perceived social support among people with mental health problems: A systematic review of recent literature Sarah Ikhtabi, Nariell Morrison, John Goulder, Zihan Ma, Amber Jarvis, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9576879/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract Background Subjective social isolation (loneliness and/or low perceived social support; PSS) is prevalent among people with mental health conditions and developing interventions to alleviate it is a priority. This systematic review provides an up-to-date synthesis of the recent evidence on the effectiveness of interventions aimed at alleviating subjective social isolation among people with mental health conditions. Methods We searched three electronic databases (Medline; PsycINFO; Web of Science) from July 2017 (the date of our group’s previous last review on this topic) to May 2025 for randomised controlled trials evaluating the effectiveness of any type of intervention that targeted subjective social isolation among people with any mental health condition. We conducted quality appraisals using the Cochrane Risk of Bias tool and used a narrative synthesis approach to summarise findings. Results A total of 40 papers, describing 39 trials including 4,474 participants, met eligibility criteria. Findings were grouped by type of mental health condition. Fifteen trials evaluating 16 types of interventions found evidence supporting the effectiveness of specific interventions: five socially-focused approaches, five cognitive behavoural therapy interventions, and six other interventions (including mindfulness-based interventions and equine-assisted therapy). Many included studies appeared to have low power or were pilot or feasibility studies. The majority of studies focused on people with common mental health conditions and recruited from community settings or through primary care services. Conclusion Our synthesis of recent literature demonstrates that some psychological approaches (such as cognitive behavioural therapy) and social interventions delivered in group settings show evidence of effectiveness in reducing subjective social isolation. Despite methodological limitations and the predominance of underpowered trials, this body of work has potential to inform further development and testing, ideally through adequately powered trials, of interventions designed to reduce loneliness and improve perceived social support among people with mental health conditions. Subjective social isolation mental health loneliness perceived social support systematic review randomised controlled trial trial Figures Figure 1 Introduction Subjective social isolation encompasses loneliness and low perceived social support (PSS) and refers to subjective negative appraisals of social relationships ( 1 , 2 ). Loneliness is a negative emotional experience characterised by a perceived discrepancy between one’s actual and desired social relationships ( 3 ). Low PSS is a negative emotional state arising from a subjective belief that one lacks adequate and sufficient sources of social and emotional support ( 1 – 3 ). Loneliness is an important public health and clinical target because of its association with poor mental health and raised prevalence among people with mental health problems ( 3 , 4 ). People with mental health conditions were found in a large UK population survey to be eight times more likely to report feeling lonely than people in the general population, increasing to 20-fold for those with multiple mental health conditions ( 5 ). Longitudinal studies indicate that loneliness is a predictor of suicidal ideation and behaviour ( 6 ), depression onset ( 4 ), and poor self-rated recovery and health related quality of life ( 7 ), and cross-sectional associations have been found between loneliness and symptom severity of depression and psychosis ( 3 , 8 ). Similarly, low PSS is associated with a range of mental health conditions, including depression and personality disorder ( 3 , 9 ). Meanwhile perceptions that social support is sufficient are associated with better self-esteem, improved quality of life, reduced risk of suicide attempt and better recovery outcomes ( 3 , 10 – 12 ). Given these negative impacts, and the high priority that mental health service users tend to attach to social connection, alleviating subjective social isolation is considered an interventional priority ( 11 , 13 ). Intervention development in this area has thus recently attracted increased interest ( 14 – 16 ). A wide range of approaches and strategies have been used to reduce loneliness, both in the general population and among people with mental health conditions ( 17 ). These included interventions focused on i) changing maladaptive cognitions, ii) building and improving social skills, iii) helping people build meaningful social connections and increase opportunities for social interaction, and iv) facilitating wider community integration ( 17 ). Across different populations, there is some evidence from two umbrella reviews supporting the effectiveness of both psychological and social interventions ( 18 , 19 ). A range of approaches to reduce subjective social isolation has also been described among people with mental health conditions, and our team has previously conducted a systematic review of the literature in 2017 ( 11 ). Of the 19 interventions identified in that review focusing on subjective social isolation, only four trials examining the following interventions among people with mental health conditions were found to be effective in improving PSS and/or loneliness: two of six trials evaluating cognitive modification, one of three trials evaluating supported socialisation, and one of four trials evaluating social skills training/psychoeducation ( 11 ). Three of the four effective interventions were delivered in specialist mental health services, and one recruited participants from a community setting. This review identified several limitations across the evidence, including a lack of large and powered trials and predominance of pilot and feasibility studies ( 11 ). As substantial further literature has been published and the need remains to identify the most effective and acceptable approaches for people with mental health conditions, an updated review is timely and necessary. To inform the development and design of future interventions and identify any interventions ready for wider implementation, we aimed to conduct a systematic review of literature published since the search date of the last systematic review on the effectiveness of interventions targeting subjective social isolation among people with mental health conditions ( 11 ). Through this review of more recent evidence, we aimed to identify effective and ineffective interventions as well as evidence gaps. Methods We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines ( 20 ) (See Additional file 1: Appendix 1) and pre-registered our review protocol on PROSPERO (Registration ID: CRD420251116121). Search Strategy We searched three electronic databases (Medline; PsycINFO; Web of Science) from July 2017 (the latest search date of the last review) to May 2025. We used the same search terms developed in our previous systematic review ( 11 ) and started our search from the final date of searching in Ma and colleagues’ review (July 2017). However, in contrast to Ma and colleagues' (2020) review, we restricted our search to focus only on interventions aimed at reducing subjective social isolation, excluding those focused on objective social isolation. Our search terms covered concepts of subjective social isolation (loneliness; PSS), mental disorders, and RCTs (see Additional File 2: Appendix 2 for detailed search terms). To identify grey literature and any missed relevant studies, we searched Google to identify any relevant dissertations or non-peer reviewed articles and Google Scholar for any additional relevant papers. We also screened reference lists of relevant systematic reviews investigating similar research questions/topics, and performed backward citation tracing to search the reference lists of included studies. Eligibility criteria Publication date We only included RCTs published from July 2017: the search date of the previous systematic review ( 11 ). Type of study design We only included RCTs of interventions aiming to reduce loneliness and/or improve PSS, as a primary or secondary outcome or one of the main outcomes, as the gold standard for evaluating effectiveness ( 21 ). We included all types of RCTs, including those described by authors as feasibility and pilot studies provided these reported between-group differences; noting the study design and statistical power when reporting findings. Population We included trials recruiting people primarily diagnosed with mental health conditions such as depression, post-traumatic stress disorder (PTSD), anxiety, personality disorders, psychosis, and bipolar disorder. Any methods of identifying participants could be used, including clinical diagnosis, validated screening scales, self-report, and use of mental health services. All age groups and geographical locations were included. We excluded trials recruiting participants primarily diagnosed with learning disabilities, autism, dementia or any other organic illnesses, substance use or physical health problems, unless these were comorbid conditions. Interventions We included trials that explicitly defined loneliness and/or PSS as the primary outcome or as one of multiple main outcomes of interest or where the interventions evaluated were clearly designed and/or aimed to address loneliness and/or PSS. We excluded studies that defined loneliness and/or PSS as a secondary outcome, without the intervention clearly targeting these factors. We included trials of interventions delivered in person, online or hybrid, and whether individual or/and group. Comparison We included studies with any type of comparison condition, including a waiting list or non-treatment control group or a group that received treatment as usual (TAU) or an active/alternative treatment. Outcomes Our primary outcome of interest was subjective social isolation (loneliness or low PSS) assessed using any validated measure. Examples of measures include the UCLA Loneliness Scale ( 22 ) and the Multidimensional Scale of Perceived Social Support (MSPSS) ( 23 ). We excluded studies that only measured objective social isolation (e.g. social network size/received social support). The following secondary outcomes were also examined, if also reported in studies included: i) symptomatic reduction for mental health condition(s) or suicidal ideation/attempt, ii) health status, iii) quality of life, and iv) service use. Data extraction All search results were exported using Covidence systematic review software ( 24 ) to manage screening. After deduplication, four reviewers (AJ, HG, ZM, IE) independently screened titles and abstracts of retrieved studies against the inclusion criteria. SI independently screened a randomly selected 10% of studies to check consistency of adherence to the criteria. Each full text of potentially eligible studies was screened by one of four reviewers (AJ, HG, IE, JG) and independently screened by one of the two second screeners (SI, ZM). Any disagreements regarding inclusion/exclusion were resolved by group discussion. NM screened the reference lists of relevant systematic reviews investigating similar research questions and conducted the grey literature search. SI conducted backward citation tracing to search the reference lists of studies included in the review. We agreed on a standardised data extraction table for study characteristics, including: author and publication year, country and study setting, participants’ characteristics, type of intervention and control group, outcome measures, effectiveness of the intervention (focusing on between group differences and group by time interactions) and risk of bias scores. For each study, one reviewer extracted data, and another reviewer independently checked extracted data for accuracy. Quality assessment We used the Cochrane Risk of Bias tool ( 25 ) to assess the quality of included studies. Each study was assessed and rated as having low, some, or high concerns for each of the following domains: sequence generation, allocation concealment, blinding of participants, personnel and outcome assessors, incomplete outcome data, selective outcome reporting, and other sources of bias. Two reviewers (of a team comprising SI, ZM, JG, NM, IE, HG, AJ) independently conducted quality appraisals for each eligible paper, discussing and resolving any discrepancies in any domain. Data synthesis We conducted a narrative synthesis of findings, based on guidelines from the ESRC’s Guidance on the Conduct of Narrative Synthesis in Systematic Reviews ( 26 ). As delineated in our protocol, we divided findings for different conditions and described outcomes for each diagnostic group. Under each mental health category, we summarised important characteristics of the interventions evaluated and trial quality ratings, then described the effectiveness of trials targeting i) loneliness ii) PSS, and iii) other outcomes, contextualising these findings in relation to statistical power (presence/absence of power calculation; adequacy of recruitment). Results After deduplication, we identified a total of 4,321 studies from our searches, of which 174 were eligible for full-text screening. Of these, 40 papers were eligible for inclusion in this review (see Figure 1 for PRISMA flowchart), including one paper that was a secondary analysis (27) of a larger trial that also met inclusion criteria for this review (28). Interrater agreement between reviewers was 90% at title/abstract screening stage and 82% at full-text screening stage, achieving 100% agreement through discussion. A summary of study characteristics including types of samples, sample characteristics, intervention types and summary of findings regarding the effectiveness of the intervention is presented in Tables 1-7 in Additional File 3, grouped by type of mental health condition. Four studies were described as pilot trials (29–32), and two as feasibility studies (33,34), although some of these reported a power calculation. We grouped included papers by the following categories of mental health conditions: depression, post-natal depression (PND), common mental health conditions ( defined as samples that consisted of people with a mixture of depression and anxiety) , social anxiety disorder, psychosis, post-traumatic stress disorder (PTSD), and mixed samples of people with a range of mental health conditions ( defined as studies among mixed samples of people with a variety of mental health conditions, including those defined as ‘any mental health condition’, or mixed samples consisting of people with a range of conditions, including mood disorders, bipolar disorder, psychotic disorders, anxiety, PTSD) . Detailed information about study characteristics (including information on descriptive and summary statistics for each study), findings on other outcomes of interest (e.g. service use, symptomatic reduction), and intervention characteristics (e.g. intervention format and duration, detailed description of intervention’ activities and aims, and intervention’s mechanism of change, if reported) is provided in Additional Files 4, and detailed risk of bias scores are presented in Additional File 5. Ten studies were judged to have some concerns about bias, and 30 were judged to have high concerns. Studies were conducted in 17 countries including the United States (US; n=14), Australia (n=4), United Kingdom (UK; n=3), Canada (n=2), Turkey (n=2), Spain (n=2), China (n=2), Netherlands (n=2), and Finland, Hong Kong, Iran, Pakistan, Norway, South Korea, Singapore, Malaysia, and Poland (n=1 from each country). A total of 4,474 participants were included, with sample sizes ranging from 18 to 666. Of the 39 interventions evaluated across 40 studies, 14 interventions were group-based, 18 were individual-based, and seven integrated both modalities. Regarding mode of delivery, 23 interventions were conducted face-to-face, 12 interventions were digital, and four were blended (digital and face-to-face). Seven studies focused on adults over the age of 50 (30,35–40), and three focused on young people between the ages of 7-18 (29,41,42). Participants were recruited from a range of settings with most studies recruiting through community settings (e.g. charities, universities, the general population) or primary care services. Nine studies recruited from mental health services, both community and inpatient. Other studies recruited through forensic settings, trauma services, and military services. A range of methods and scales were used to identify mental health conditions; details are shown in Additional file 4. The majority of studies measured loneliness using the UCLA Loneliness Scale. Other measures of loneliness and a range of measures were used to assess PSS across studies included (See Additional File 4: Appendix 4 for measures used in each study). We also extracted data on our secondary outcomes of interest (e.g. symptomatic reduction for mental health condition(s), health status). A full list of measures used in each study are described in Appendix 5 (See Additional File 4). Interventions for people with depression Eleven studies focused on people with depression. Studies were conducted in the United States (n=5), and Canada, Hong Kong, Turkey, Iran, and Spain (one from each country). Three interventions were digital interventions, five were face-to-face, and two were blended interventions (face-to-face and digital). Duration of interventions ranged from four weeks to six months. Seven trials measured loneliness and seven trials measured PSS, including three assessing both outcomes (27,28,39). Felton et al. (2019) analysed data from a sub-sample of participants in the trial by Johnson et al. (2019). Sample sizes ranged from 18 to 181 participants with a predominately female range in all studies. One study recruited inpatients (43), two drew on the same sample of incarcerated people(27,28), one recruited from mental health services (30) and the remainder recruited from primary care or community settings. Six studies were judged to have high risk of bias due to methodological concerns, primarily related to outcome measurement (n=4). Other concerns related to: reporting selected findings (n=1), handling of missing data (n=1), and deviation from intended intervention (n=1). a) Loneliness as outcome Of the seven trials in samples with depression, two (one group-based and one individual-based) reported evidence supporting the effectiveness of the intervention. A large statistically significant effect was reported for a community-based group activities intervention even though the study did not achieve the intended sample size (39) and for a fully powered telephone-based individual relational intervention (although this study was a post-hoc analysis of a subset of participants who met criteria for depression) (45). All trials were fully powered, apart from those reported by Joo et al. (2025), which did not achieve the intended sample size, Felton et al. (2019), a subgroup analysis of a larger trial, and Van Orden et al. (2021), a pilot trial that reported a power calculation but did not meet its intended sample size. b) PSS as outcome Seven trials measured PSS. Moeini et al. (2019) reported that an individual-based online CBT intervention showed evidence of an effect on PSS, although the study did not achieve the sample size required by the power calculation. Conley et al. (2024) also showed evidence of effectiveness for a group-based interpersonal psychotherapy intervention: this was a pilot trial with a sample of only 18 however the difference nonetheless reached statistical significance. For five trials, the intervention evaluated was not found to be effective. Interventions included an individual solution focused intervention (43), a group spiritual connectivity intervention (46), a mixed (group and individual-based) interpersonal psychotherapy intervention (27,28), and a community-based group activities intervention (39). Two of these trials were fully powered (28,43), two did not meet their target sample size (39,46), and one was a subgroup analysis (27). c) Other outcomes of interest Of the 11 trials included in this category of findings, eight trials reported significant reductions in symptoms of depression (27,28,30,32,42–44,46) , and one reported significant improvement in social-emotional quality of life (30). Interventions for women with post-natal depression (PND) Six trials investigated interventions for women with PND. Studies were conducted in the UK, US, China, Canada, South Korea, and Singapore (n=1 from each country). Five were digital interventions, and one was face-to-face. Duration of interventions ranged from four weeks to three months. Two trials measured loneliness, and five measured PSS, of which one assessed both (47). Sample sizes ranged from 61 to 150 participants. All recruited from community settings or primary care. Five trials were judged to have high risk of bias, largely due to concerns regarding the handling of missing data and outcome measurement. a) Loneliness as outcome We identified two trials that evaluated socially focused programmes, both fully powered. Evidence was reported to support the effectiveness of a group-based online songwriting intervention (48). There was no evidence to support the effectiveness of an individual-based peer support digital intervention (47). b) PSS as outcome Of five trials in this category, one fully powered RCT evaluating a mixed (individual and group-based) digital intervention based on mindfulness and social networking reported evidence to support the effectiveness of the intervention (49). Four trials reported no evidence to support effectiveness of a group-based parenting programme incorporating psychoeducation (33), an individual-based online psychoeducation intervention (50), an individual-based digital CBT intervention (51) or an individual-based digital peer support intervention (47). Two trials included in this category were fully powered (47,51), while Boyd et al. (2017), a feasibility study that reported on differences between the intervention and wait-list condition, did not achieve the intended sample size and Dol et al. (2025), a study that only reported outcomes at six month follow-up was initially fully powered but did not achieve target follow-up rates. c) Other outcomes of interest Of the six trials in PND populations, three trials reported reduction in symptoms of depression (47–49). Interventions for people with common mental health conditions Five trials focused on groups of people with common mental health problems (a mixture of depression and anxiety). Studies were conducted in Australia, Spain, Poland, Malaysia and China (n=1 from each country). One intervention was digital, another was a blended intervention (face-to-face and digital), and the rest were face-to-face. Duration of interventions ranged from two weeks to four months. Four trials measured loneliness, and one trial measured PSS. Sample sizes ranged from 34 to 133 participants and four studies had a majority of female participants and four recruited individuals over 60 years old. One study recruited from residential care (36) and another via electronic medical records (38), with the rest recruiting from community settings. All five studies were judged to be at high risk of bias due to methodological concerns, largely related to the outcome measurement (n= 3) and handling of missing data (n=3). Other concerns included potential biases due to: randomisation process (n=1); deviations from intended interventions (n=2); and selective outcome reporting (n=1). a) Loneliness as outcome Two of four trials with loneliness as an outcome reported evidence of effectiveness. These were a community group-based CBT intervention (40) and an individual and group-based counselling and psychoeducation intervention (37); although both these studies did not report a power calculation and one underrecruited due to COVID-19 restrictions (37). Two trials reported no statistically significant differences between intervention and control groups: one evaluating a group-based spiritual reminiscence interpersonal therapy intervention (36) and one an individual-based agent-guided CBT intervention delivered via chat-bot (52). Both these studies exceeded their target sample size but only Syed (2017) based this on a power calculation. b) PSS as outcome A trial with PSS as an outcome reported that a group-based, moderate-intensity physical activity programme was effective, although the intended sample size was not achieved (38). c) Other outcomes of interest Of the five trials included in this category of findings, three reported significant reductions in symptoms of depression and anxiety (37,38,40). One trial reported a significant improvement in perceived health status (38). Interventions for people with social anxiety disorder Two trials from the U.S focused on social anxiety and measured loneliness as a main outcome (53,54). One was a face-to-face intervention (53) and the other was blended (digital and face-to-face) (54). Duration of interventions ranged from four to twelve weeks and the sample size was 55 to 108 participants. One study included a predominantly female sample (54). One study included recruitment from clinical referrals (53) and the other recruited from community settings (54). Both studies were judged to have a high risk of bias due to methodological concerns related to the measurement of outcomes. a) Loneliness as outcome One of the two trials in this category reported that the study intervention was effective. A three-arm trial compared two active group-based interventions (a group-based CBT intervention and a group-based mindfulness-based stress reduction (MBSR) intervention) and a waitlist control group (53). There was no significant difference in loneliness between the CBT and MBSR interventions, but loneliness was significantly lower for both these interventions compared to the waitlist controls. The authors did not report a power calculation. A fully-powered trial evaluating a digital individual-based multi-component intervention targeting fear of intimacy found no evidence of effectiveness (54). b) Other outcomes of interest None of the trials of interventions for people with social anxiety disorder reported that interventions were effective for anxiety symptoms. Interventions for people with psychosis Four trials focused on people with psychosis. Studies were conducted in the UK, Turkey, Australia and the Netherlands (n=1 from each). All were face-to-face except for one digital intervention (55). Duration of treatment ranged from five weeks to eighteen months. Four trials measured loneliness and two measured both loneliness and PSS (55,56). Sample sizes ranged from 40 to 170 participants. Three studies had samples consisting of approximately equal numbers of males and females and one had a predominately male sample (56). All studies recruited participants with psychosis from mental health services. One study was rated as having some concern for risk of bias (55), and three trials were judged to be at high risk of bias, mainly due to concerns regarding outcome measurement (n=3) and deviations from intended intervention (n=2). a) Loneliness as outcome Of four included trials, one individual-based intervention evaluating an equine-assisted therapy reported evidence of effectiveness (57). Although this study reported a power calculation, the intended sample size was not achieved. A feasibility study compared Groups for Health (G4H) in its usual group format with individual-based G4H. G4H is a psychological intervention that includes a supported socialisation element and draws on social identity theory. The study found no statistically significant difference between the two G4H conditions; however, this study was intended to test feasibility of a full trial and was not powered to find a significant effect (31). Two trials found no evidence to support the effectiveness of a mixed (individual and group-based) peer support and online social therapy programme (55) or a mixed (individual and group-based) peer support eating club intervention (56) but both were underpowered with the intended sample size not achieved. b) PSS as outcome The above trials without evidence of a significant effect on loneliness (55,56) also found no evidence of an effect on PSS. c) Other outcomes of interest Of four trials in this category of findings, one study reported a significant reduction in positive symptoms of psychosis and significant improvement in quality of life (57). One study assessing use of emergency services reported significantly lower rates of emergency service use in the intervention group compared to the control group (55). Interventions for people with PTSD Four trials focused on people with PTSD. Studies were conducted in the United States (n=2), Pakistan (n=1), and Norway (n=1). All interventions were delivered face-to-face. Two interventions lasted three months and duration was unreported in the other two studies (41,58). Sample sizes ranged from 75 to 162 participants. Two studies recruited predominately male samples of veterans and two studies focused on children. One study was rated as having some concern for risk of bias (29). Three studies were judged to have high risk of bias due to methodological concerns related to measurement of outcomes (n=2) and potential deviation from the intended intervention (n=1). a) PSS as an outcome All four trials in this category focused on PSS rather than loneliness. An RCT of an individual-based prolonged exposure therapy intervention (59) and another pilot trial of a group-based CBT intervention reported the intervention to be effective (29); despite each having small samples and no power calculation. There was no significant evidence of effect for an individual-based trauma-focused CBT intervention (41) or for an individual-based behavioural activation psychotherapy intervention (58), but both were underpowered. b) Other outcomes of interest Of the four trials included in this category of findings, three studies reported evidence of a significant reduction in symptoms of PTSD (41,59) of which one was a small pilot trial (29). Interventions for mixed samples of people with a variety of mental health conditions Eight trials recruited samples of people with a variety of mental health conditions. Studies were conducted in the US (n=3), the UK (n=1), Australia (n=2), Finland (n=1) and the Netherlands (n=1). Two interventions were digital, and the rest were face-to-face. Duration of interventions ranged from a single session to three years. Seven trials measured loneliness and two trials measured PSS, including one trial which measured both (60). Sample sizes ranged from 40 to 335 participants. The majority of studies (n=6) had samples consisting of 60% or more female participants. Two studies recruited participants from community settings (61,62), and others from health service settings (34,63–65). Two studies were judged to have some concerns about bias, whilst six studies were judged to be at high risk of bias, mainly due to methods for measuring outcomes (n=6), missing outcomes (n=4), randomisation process (n=1), or selective outcome reporting (n=1). a) Loneliness as outcome One of the seven studies with mixed samples reported evidence of effectiveness. A fully powered trial evaluating the effectiveness of the Groups 4 Health (G4H) intervention reported a significant reduction in loneliness in the G4H group compared to treatment as usual (62). A feasibility trial of an individual and group-based peer-delivered supported socialisation intervention (Community Navigators) found no statistically significant difference in outcomes between an experimental group receiving the intervention and a treatment as usual control, but this trial was primarily conducted to test feasibility of conducting a full trial and was not powered to detect a difference (34). An individual-based intervention combining psychoeducation and cognitive bias modification showed significant reductions in thwarted belongingness in the intervention group compared to treatment as usual; however this study was a post-hoc exploratory sub-analysis of a small subgroup of a larger trial and was underpowered (66). Four trials found no evidence to support the effectiveness of an individual-based caring-contact intervention (63), an individual and group-based peer-delivered community participation programme (64), the Groups 4 Health intervention (61) or an individual-based social skills support and supported socialisation programme (60). Two of these trials were fully powered (61,63), while one (64) did not report a power calculation, and one (60) did not achieve its target sample size and reported high dropout rates. b) PSS as outcome Two trials measured PSS. There was no evidence of any difference in effectiveness between a long-term individual-based psychodynamic psychotherapy intervention, short-term psychodynamic therapy and short-term solution focused therapy in a three-arm trial (65) or between a supported socialisation programme and control group (60). One study did not achieve its target sample size (60) and the other study did not report a power calculation but reported achieving a large sample size (65). c) Other outcomes of interest Of the eight trials conducted with mixed samples, one trial reported that the intervention evaluated led to significant improvements in symptoms of social anxiety (62) and one reported a small but significant decrease in suicidal ideation (63). Two studies reported a decrease in service use and duration of psychiatric admission (60,62). Discussion Our findings suggest that, based on trials published from 2017–2025, some psychologically-focused interventions (including cognitive behavioural/modification approaches and mindfulness-based interventions), and some supported socialisation/socially focused interventions delivered in group settings are effective at reducing loneliness and/or improving PSS. Recruitment in these studies was from a wide range of settings, including community settings, primary care and mental health services. Of the 40 studies of 39 interventions included in this review of recent trials, 15 studies (evaluating 16 types of interventions) reported significant improvements in PSS and/or loneliness. These interventions included: five involving supported socialisation/socially focused interventions (e.g. support in engaging in social activities)( 38 , 39 , 44 , 48 , 62 ) (one of which was based on a psychological theory of loneliness: social identity theory ( 62 )), five CBT interventions ( 29 , 40 , 42 , 53 , 66 ), and one of each of the following: a mixed intervention integrating a social networking component and mindfulness techniques ( 49 ), an intervention combining individual counselling and group psychoeducational sessions ( 37 ), a MBSR intervention ( 53 ), prolonged exposure therapy ( 59 ), interpersonal psychotherapy ( 32 ), and equine-assisted therapy( 57 ) (See Additional File 4 Appendix 6 for characteristics of interventions evaluated in this review). One trial of a community-based group activities interventions reported positive effects of the intervention for loneliness but not PSS among people with depression ( 39 ). Regarding negative findings, of the 40 included studies, a total of 9 fully powered trials (evaluating 10 types of interventions) reported no group differences in PSS and/or loneliness. These interventions were: i) six types of psychological interventions including an interpersonal psychotherapy intervention ( 28 ), a behavioural activation intervention ( 45 ), a solution focused intervention ( 43 ), a CBT intervention ( 51 ), a spiritual reminiscence interpersonal therapy intervention ( 36 ), and a multi-component intervention targeting fear of intimacy ( 54 ), and ii) three interventions involving supported socialisation/socially focused or relational or individual peer support approaches (See Additional File 4 Appendix 6 for characteristics of interventions evaluated in this review). A total of 12 underpowered trials and one pilot and two feasibility studies reported negative findings of which six were supported socialisation/socially focused interventions ( 31 , 35 , 55 , 56 , 60 , 64 ) and nine were psychologically focused interventions ( 27 , 30 , 33 , 41 , 46 , 50 , 52 , 58 , 65 ). As these findings were based on underpowered trials, we cannot draw any clear conclusions regarding the effectiveness of these interventions. Most studies recruited from the general population or primary care. Only nine studies recruited participants from mental health services, and of these, only one reported positive results for an equine-assisted intervention for people with psychosis ( 57 ). Although we sought to identify types of interventions that might be effective for people with specific mental health conditions (e.g. depression, PTSD), no clear pattern emerged regarding which types of interventions work best for specific clinical groups. Furthermore, the interventions, their intended mechanisms of action (See Additional File 4) and target populations varied greatly between studies. We therefore decided that neither meta-analysis nor GRADE ratings of confidence in findings were appropriate. Overall, this heterogeneity between studies, the low methodological quality of many included studies, and predominance of underpowered trials (including pilot studies) restricted our ability to draw robust and clear conclusions regarding which types of interventions are most effective in the context of different types of mental health conditions. Comparing the findings of the previous review ( 11 ) (covering the 19 eligible trials published until 2017 that focused on subjective social isolation) and our review (covering the 40 eligible trials published from 2017–2025), both draw similar conclusions. This was despite the proliferation of trial publications over the more recent period, and the assumption that trial methods might have improved over that time. Both reviews conclude that it is not possible to determine the most effective treatment approaches from the evidence included in each synthesis, nor what may work best for different clinical groups. However, our review of more recent literature did, in contrast to the previous review, identify a number of social and psychosocial interventions with some evidence of effectiveness. In most cases, each intervention was supported by only one trial, with trials often of limited quality and scale. We therefore view these trials as a starting point for further work, including good quality replication studies, to test and establish whether these interventions are ready for wider implementation. Several social interventions (primarily tested in underpowered trials) were ineffective, and the reasons for this remain unclear, although this is likely attributable to the lack of fully powered trails evaluating these interventions. People with mental health conditions experience difficulties in forming and maintaining social connections resulting from a range of societal barriers (e.g. social exclusion) ( 17 , 67 ). Mechanistically, socially focused interventions may offer individuals opportunities to engage in social groups/activities and develop positive social connections and group membership that then reduce feelings of loneliness and promote a sense of belonging and social inclusion ( 14 , 68 ). Our provision of further detail about intervention descriptions, components/activities, and characteristics (see Additional file 4: Appendix 6) will provide those engaged in theory of change and/or intervention development with further clues as to likely pathways. Our review also identified some recent evidence supporting the effectiveness of cognitive behavioural approaches for addressing loneliness and/or PSS. This is supported by preliminary findings from a previous systematic review and a narrative review focused on people with mental health conditions (covering studies published since inception), which suggested that interventions focused on addressing and changing maladaptive social cognitions are effective at reducing subjective social isolation in people with mental health conditions ( 11 , 17 ). For psychological interventions in general, we identified a small number (n = 4) of recent studies reporting the effectiveness of psychologically-based interventions such as mindfulness-based approaches ( 49 , 53 ). However, negative findings were reported for several psychological interventions evaluated in nine underpowered trials and six fully-powered trials. It is also worth noting that some recently published studies in our review reported improvement in mental health outcomes but no positive effects on PSS and loneliness ( 28 , 30 , 41 , 43 , 46 , 47 ). This might indicate that loneliness and PSS are difficult to shift even when interventions successfully improve other outcomes. Overall, our synthesis of recent evidence, primarily based on underpowered trials, identified a range of social and psychological interventions that may be effective at reducing loneliness and improving perceived social support; serving as a basis for further work to test their effectiveness in diverse settings and clinical groups, using adequately powered trials. Negative findings were reported for several interventions and interventions widely varied thereby making it difficult to identify conclusive patterns regarding what types of interventional approach are most effective. Strengths and limitations We conducted a systematic review of studies published after July 2017, adhering to the PRISMA guidelines, synthesising the recent evidence on the effectiveness of interventions aiming to reduce subjective social isolation among people with different mental health conditions, focusing on RCTs as the gold standard for testing effectiveness. However, there are a number of limitations to consider in interpreting our findings. We decided to only include trials that focused on subjective social isolation as a primary/one of the main outcomes and where the interventions evaluated clearly focused on reducing subjective social isolation. This meant that we excluded interventional trials that were not designed to clearly target subjective social isolation, even if they did provide evidence of effectiveness in reducing it. Furthermore, the heterogeneity of included studies regarding types of interventions, study participants, and settings led to our reliance on a narrative synthesis approach and meant that meta-analysis was inappropriate. Moreover, some of the studies reporting significant effects had small sample sizes and were underpowered, raising the possibility of Type 1 errors ( 69 ). Finally, this review only focused on studies conducted from July 2017 onwards, which meant that our synthesis did not include earlier research findings. Research and clinical implications The main implications that can be drawn from these findings for policymakers relate to policies for people with mild/moderate psychiatric symptoms primarily recruited from community settings/services, educational settings, and primary health care services; the samples used in the majority of studies. Based on our findings for these groups, there are grounds for further testing social interventions and psychological interventions such as CBT focused on addressing subjective social isolation, delivered in group settings. Where interventions included in our review show evidence of some effectiveness, larger-scale studies that are fully powered and of high quality would be helpful to understand whether they are indeed effective. These studies would benefit from also evaluating whether these interventions have an impact on mental health outcomes/symptoms and overall quality of life. Importantly, an important evidence gap remains for people with more severe mental health illness, such as psychosis, and secondary mental health service users for which there were few good quality trials, and for whom we know the experience of loneliness to be debilitating ( 70 ). Future research should address the quality issues in such trials complemented by studies to explore acceptable approaches, particularly for co-developed interventions tailored to the specific social needs of people with different mental health conditions. Future refinements of such interventions should be informed by a clearly defined theory of change, evaluated for acceptability, and trialled using adequately powered and rigorously designed RCTs. Our findings, based on recent evidence, indicate that both social and psychological interventions may have potential to reduce subjective social isolation, as well as interventions that may be hybrids of both approaches, such as Groups 4 Health. In other populations including the general population, a wide range of psychological and social interventions have also been trialled, with a recent umbrella review suggesting that psychological interventions may be more effective for loneliness, although with positive reports also for some mixed interventions ( 16 ). Little work so far allows conclusions to be drawn about what works best for whom, and it may be that, as suggested by Eager et al.’s (2024) qualitative findings, psychological strategies are more suitable for long-term loneliness and social strategies for transient and situational loneliness ( 71 ). In further research, attention should be given to developing theoretically informed interventions with clear pathways, incorporating input from people with relevant lived experience, and informed by the increasing body of evidence on potential causes of loneliness among people with mental health conditions; all of which would help in developing effective interventions ( 71 ). In planning and conducting these trials, it is important to address common methodological issues that impact the rigor and credibility of findings, noted in our review, such as a neglect of power considerations. Strategies are also needed to minimise high attrition rates (particularly in the event of future pandemics) and handle missing outcomes. Pending further evaluations and adaptations of interventions identified as potentially effective in this review and more definitive trial evidence, and given that connectedness is a highly valued recovery outcome among people with mental health conditions ( 13 ), it is important for mental health practitioners to ask about subjective social isolation in practice and consider patient-centered means of addressing this. There may also be practice insights and pointers/directions for further intervention development to be gained from trials focused on general population samples. For instance, there is systematic review evidence to support the effectiveness of CBT, mindfulness-based interventions, and interventions based on social identity theory; with the most consistent evidence supporting the use of CBT ( 72 – 74 ). Conclusions Our comprehensive systematic review of recent trials (published from 2017–2025) identified 40 studies evaluating interventions aimed at reducing subjective social isolation among people with mental health conditions. Our synthesis provided preliminary evidence to suggest that interventions involving supported socialisation and social group activities and psychological interventions such as cognitive behavioural therapy addressing maladaptive social cognitions may be effective in alleviating subjective social isolation in some contexts and clinical groups, but firm conclusions rely on replicability and higher quality studies. The low methodological quality of these trials and lack of well-powered trials therefore limited our ability to make definitive conclusions and specific recommendations for practice. Despite our efforts to identify which types of interventions are most effective for different types of mental health conditions, the lack of robust evidence meant that we could not determine from this recent evidence which interventions and interventional components are most effective for different clinical groups particularly for people with severe mental health conditions. Future research should develop theoretically-driven and acceptable interventions targeting subjective social isolation tailored to the social needs of people with specific psychiatric diagnoses and evaluate their effectiveness using fully-powered and rigorously designed RCTs. Abbreviations CBT: Cognitive Behavioural Therapy MBSR: Mindfulness-Based Stress Reduction N: Number of participants PND: Post-Natal Depression PRISMA: Preferred Reporting Items for Systematic Reviews and Meta-Analyses PTSD: Post Traumatic Stress Disorder PSS: Perceived Social Support RCT: Randomised Controlled Trial TAU: Treatment As Usual UK: University Kingdon US: United States UCLA: University of California, Los Angeles Declarations Ethics approval and consent to participate: Not Applicable Consent for publications: Not Applicable Availability of data and materials: All data analysed during this study are included in this published article and its supplementary information files. No new datasets were generated. Therefore, data sharing is not applicable. Competing interests: The authors declare that they have no competing interests. Funding: We acknowledge salary support for SI, AP, BLE, and SJ from the National Institute for Health and Care Research (NIHR) University College Hospitals London (UCLH) Biomedical Research Centre (BRC) for funding the activities of the Loneliness and Social Isolation in Mental Health Research Network. This funding source had no direct involvement in the review design, analysis, decision to publish or preparation and submission of the manuscript. Authors’ contributions: SI, BLE, AP, and SJ collaboratively developed the research protocol. AJ, HG, ZM, and IE screened titles and abstracts of all potentially relevant papers identified from the databases. SI independently screened the titles and abstracts of randomly selected 10% of papers. The full texts were independently co-screened by one of four reviewers (AJ, HG, IE, JG) paired with one of two co-screeners (SI, ZM). 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Supplementary Files AdditionalFile1.docx Additional Files File name: Additional file 1 File format: Word document (docx) Title of data: Appendix 1: PRISMA Checklist Description of data: Additional file 1 presents the PRISMA checklist for reporting systematic reviews AdditionalFile2.docx File name: Additional file 2 File format: Word document (docx) Title of data: Appendix 2: Search Terms Description of data: Additional file 2 presents the search terms used in this review AdditionalFile3.docx File name: Additional file 3 File format: Word document (docx) Title of data: Additional File 3: Appendix 3: Summary tables of study characteristics grouped by mental health conditions Description of data: Additional file 3 (Appendix 3) presents summary tables of study characteristics and findings grouped by mental health condition AdditionalFile4.docx File name: Additional file 4 File format: Word document (docx) Title of data: Additional File 4: Detailed characteristics of trials, findings of other outcomes on interest, and characteristics of interventions Description of data: Additional file 4 (Appendices 4-6) presents i) tables with detailed characteristics of trials and descriptive and summary statistics for trials assessing loneliness or/and perceived social support grouped by mental health condition, ii) table of characteristics of included studies assessing other outcomes of interest including symptoms of mental health, service use, quality of life, and health status, and iii) table of characteristics of interventions evaluated in included studies and their mechanism of change. AdditionalFile5.docx File name: Additional file 5 File format: Word document (docx) Title of data: Additional file 5: Quality assessments Description of data: Additional file 5 presents detailed risk of bias scores for included studies Cite Share Download PDF Status: Under Review Version 1 posted Reviewers invited by journal 06 May, 2026 Editor invited by journal 05 May, 2026 Editor assigned by journal 01 May, 2026 Submission checks completed at journal 01 May, 2026 First submitted to journal 30 Apr, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Ikhtabi","email":"data:image/png;base64,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","orcid":"","institution":"University College London","correspondingAuthor":true,"prefix":"","firstName":"Sarah","middleName":"","lastName":"Ikhtabi","suffix":""},{"id":635271290,"identity":"430ae513-886f-4687-a19c-d08addfbf4ee","order_by":1,"name":"Nariell Morrison","email":"","orcid":"","institution":"University College London","correspondingAuthor":false,"prefix":"","firstName":"Nariell","middleName":"","lastName":"Morrison","suffix":""},{"id":635271292,"identity":"f42772d7-5313-4c51-96c4-41653c57214a","order_by":2,"name":"John Goulder","email":"","orcid":"","institution":"University College London","correspondingAuthor":false,"prefix":"","firstName":"John","middleName":"","lastName":"Goulder","suffix":""},{"id":635271293,"identity":"d743d9b9-e4fa-4191-8681-725b91972b01","order_by":3,"name":"Zihan Ma","email":"","orcid":"","institution":"University College London","correspondingAuthor":false,"prefix":"","firstName":"Zihan","middleName":"","lastName":"Ma","suffix":""},{"id":635271295,"identity":"32686332-d928-41c2-9317-3bdcbcb3135a","order_by":4,"name":"Amber Jarvis","email":"","orcid":"","institution":"University College London","correspondingAuthor":false,"prefix":"","firstName":"Amber","middleName":"","lastName":"Jarvis","suffix":""},{"id":635271297,"identity":"9f133dde-cefa-4812-8510-8019492ab05b","order_by":5,"name":"Isobel Emptage","email":"","orcid":"","institution":"University College London","correspondingAuthor":false,"prefix":"","firstName":"Isobel","middleName":"","lastName":"Emptage","suffix":""},{"id":635271298,"identity":"0b2a0ef1-55a7-4a25-90d5-f8631bcc7025","order_by":6,"name":"Hannah Gray","email":"","orcid":"","institution":"University College London","correspondingAuthor":false,"prefix":"","firstName":"Hannah","middleName":"","lastName":"Gray","suffix":""},{"id":635271299,"identity":"ff8b632e-52d1-4f17-b1c9-c47af501daf3","order_by":7,"name":"Alexandra Pitman","email":"","orcid":"","institution":"University College London","correspondingAuthor":false,"prefix":"","firstName":"Alexandra","middleName":"","lastName":"Pitman","suffix":""},{"id":635271301,"identity":"e6237cf2-6830-4f99-86f7-fae9de63f9c3","order_by":8,"name":"Brynmor Lloyd-Evans","email":"","orcid":"","institution":"University College London","correspondingAuthor":false,"prefix":"","firstName":"Brynmor","middleName":"","lastName":"Lloyd-Evans","suffix":""},{"id":635271303,"identity":"d52cb2d7-d2ce-48d0-bfaa-13ccd02301db","order_by":9,"name":"Sonia Johnson","email":"","orcid":"","institution":"University College London","correspondingAuthor":false,"prefix":"","firstName":"Sonia","middleName":"","lastName":"Johnson","suffix":""}],"badges":[],"createdAt":"2026-04-30 11:54:46","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9576879/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9576879/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":109286802,"identity":"ba3c65ac-6f11-4c4e-838c-7b370fa62dcb","added_by":"auto","created_at":"2026-05-15 02:37:19","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":52321,"visible":true,"origin":"","legend":"\u003cp\u003eFlow chart of studies through the systematic review process\u003c/p\u003e","description":"","filename":"OnlinePRISMAFlowChart.png","url":"https://assets-eu.researchsquare.com/files/rs-9576879/v1/4abff2d4e514ce0eeb0e3c2e.png"},{"id":109297307,"identity":"c2b80df2-d782-4f94-8285-3f578870ff0e","added_by":"auto","created_at":"2026-05-15 08:55:57","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":360797,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9576879/v1/528046d4-65cb-4f63-a68b-6dca9b3a3821.pdf"},{"id":109296059,"identity":"bdd0a4d2-de01-4b99-91bb-f73198ee7754","added_by":"auto","created_at":"2026-05-15 08:45:03","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":276460,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAdditional Files\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFile name: Additional file 1\u003c/p\u003e\n\u003cp\u003eFile format: Word document (docx)\u003c/p\u003e\n\u003cp\u003eTitle of data: Appendix 1: PRISMA Checklist\u003c/p\u003e\n\u003cp\u003eDescription of data: Additional file 1 presents the PRISMA checklist for reporting systematic reviews\u003c/p\u003e","description":"","filename":"AdditionalFile1.docx","url":"https://assets-eu.researchsquare.com/files/rs-9576879/v1/b2b4f34ddff3e6ce81d7e711.docx"},{"id":109286804,"identity":"3eed7b1e-f8f6-4da2-9c61-c022e455884d","added_by":"auto","created_at":"2026-05-15 02:37:19","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":19429,"visible":true,"origin":"","legend":"\u003cp\u003eFile name: Additional file 2\u003c/p\u003e\n\u003cp\u003eFile format: Word document (docx)\u003c/p\u003e\n\u003cp\u003eTitle of data: Appendix 2: Search Terms\u003c/p\u003e\n\u003cp\u003eDescription of data: Additional file 2 presents the search terms used in this review\u003c/p\u003e","description":"","filename":"AdditionalFile2.docx","url":"https://assets-eu.researchsquare.com/files/rs-9576879/v1/e8be7aa7ca6363fb2e941942.docx"},{"id":109286806,"identity":"6d01603a-6e70-49bc-98eb-f3b382c11806","added_by":"auto","created_at":"2026-05-15 02:37:19","extension":"docx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":68795,"visible":true,"origin":"","legend":"\u003cp\u003eFile name: Additional file 3\u003c/p\u003e\n\u003cp\u003eFile format: Word document (docx)\u003c/p\u003e\n\u003cp\u003eTitle of data: Additional File 3: Appendix 3: Summary tables of study characteristics grouped by mental health conditions\u003c/p\u003e\n\u003cp\u003eDescription of data: Additional file 3 (Appendix 3) presents summary tables of study characteristics and findings grouped by mental health condition\u003c/p\u003e","description":"","filename":"AdditionalFile3.docx","url":"https://assets-eu.researchsquare.com/files/rs-9576879/v1/e6d6fa6993c693549ca1cb42.docx"},{"id":109286805,"identity":"8a1d87f1-f3b7-4633-9130-e449a952c11c","added_by":"auto","created_at":"2026-05-15 02:37:19","extension":"docx","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":176552,"visible":true,"origin":"","legend":"\u003cp\u003eFile name: Additional file 4\u003c/p\u003e\n\u003cp\u003eFile format: Word document (docx)\u003c/p\u003e\n\u003cp\u003eTitle of data: Additional File 4: Detailed characteristics of trials, findings of other outcomes on interest, and characteristics of interventions\u003c/p\u003e\n\u003cp\u003eDescription of data: Additional file 4 (Appendices 4-6) presents i) tables with detailed characteristics of trials and descriptive and summary statistics for trials assessing loneliness or/and perceived social support grouped by mental health condition, ii) table of characteristics of included studies assessing other outcomes of interest including symptoms of mental health, service use, quality of life, and health status, and iii) table of characteristics of interventions evaluated in included studies and their mechanism of change.\u003c/p\u003e","description":"","filename":"AdditionalFile4.docx","url":"https://assets-eu.researchsquare.com/files/rs-9576879/v1/542ea5192bcf6bc3209efae8.docx"},{"id":109286807,"identity":"4bd8249e-5922-470b-838b-c04fd2063fd8","added_by":"auto","created_at":"2026-05-15 02:37:19","extension":"docx","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":24230,"visible":true,"origin":"","legend":"\u003cp\u003eFile name: Additional file 5\u003c/p\u003e\n\u003cp\u003eFile format: Word document (docx)\u003c/p\u003e\n\u003cp\u003eTitle of data: Additional file 5: Quality assessments\u003c/p\u003e\n\u003cp\u003eDescription of data: Additional file 5 presents detailed risk of bias scores for included studies\u003c/p\u003e","description":"","filename":"AdditionalFile5.docx","url":"https://assets-eu.researchsquare.com/files/rs-9576879/v1/58d96c5661a4591f2bc9cecd.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"The effectiveness of interventions for reducing loneliness and improving perceived social support among people with mental health problems: A systematic review of recent literature","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSubjective social isolation encompasses loneliness and low perceived social support (PSS) and refers to subjective negative appraisals of social relationships (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e). Loneliness is a negative emotional experience characterised by a perceived discrepancy between one\u0026rsquo;s actual and desired social relationships (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e). Low PSS is a negative emotional state arising from a subjective belief that one lacks adequate and sufficient sources of social and emotional support (\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eLoneliness is an important public health and clinical target because of its association with poor mental health and raised prevalence among people with mental health problems (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e). People with mental health conditions were found in a large UK population survey to be eight times more likely to report feeling lonely than people in the general population, increasing to 20-fold for those with multiple mental health conditions (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e). Longitudinal studies indicate that loneliness is a predictor of suicidal ideation and behaviour (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e), depression onset (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e), and poor self-rated recovery and health related quality of life (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e), and cross-sectional associations have been found between loneliness and symptom severity of depression and psychosis (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e). Similarly, low PSS is associated with a range of mental health conditions, including depression and personality disorder (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e). Meanwhile perceptions that social support is sufficient are associated with better self-esteem, improved quality of life, reduced risk of suicide attempt and better recovery outcomes (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eGiven these negative impacts, and the high priority that mental health service users tend to attach to social connection, alleviating subjective social isolation is considered an interventional priority (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e). Intervention development in this area has thus recently attracted increased interest (\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eA wide range of approaches and strategies have been used to reduce loneliness, both in the general population and among people with mental health conditions (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e). These included interventions focused on i) changing maladaptive cognitions, ii) building and improving social skills, iii) helping people build meaningful social connections and increase opportunities for social interaction, and iv) facilitating wider community integration (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e). Across different populations, there is some evidence from two umbrella reviews supporting the effectiveness of both psychological and social interventions (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eA range of approaches to reduce subjective social isolation has also been described among people with mental health conditions, and our team has previously conducted a systematic review of the literature in 2017 (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e). Of the 19 interventions identified in that review focusing on subjective social isolation, only four trials examining the following interventions among people with mental health conditions were found to be effective in improving PSS and/or loneliness: two of six trials evaluating cognitive modification, one of three trials evaluating supported socialisation, and one of four trials evaluating social skills training/psychoeducation (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e). Three of the four effective interventions were delivered in specialist mental health services, and one recruited participants from a community setting. This review identified several limitations across the evidence, including a lack of large and powered trials and predominance of pilot and feasibility studies (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e). As substantial further literature has been published and the need remains to identify the most effective and acceptable approaches for people with mental health conditions, an updated review is timely and necessary.\u003c/p\u003e \u003cp\u003eTo inform the development and design of future interventions and identify any interventions ready for wider implementation, we aimed to conduct a systematic review of literature published since the search date of the last systematic review on the effectiveness of interventions targeting subjective social isolation among people with mental health conditions (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e). Through this review of more recent evidence, we aimed to identify effective and ineffective interventions as well as evidence gaps.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eWe followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e) (See Additional file 1: Appendix 1) and pre-registered our review protocol on PROSPERO (Registration ID: CRD420251116121).\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eSearch Strategy\u003c/h2\u003e \u003cp\u003eWe searched three electronic databases (Medline; PsycINFO; Web of Science) from July 2017 (the latest search date of the last review) to May 2025. We used the same search terms developed in our previous systematic review (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e) and started our search from the final date of searching in Ma and colleagues\u0026rsquo; review (July 2017). However, in contrast to Ma and colleagues' (2020) review, we restricted our search to focus only on interventions aimed at reducing subjective social isolation, excluding those focused on objective social isolation. Our search terms covered concepts of subjective social isolation (loneliness; PSS), mental disorders, and RCTs (see Additional File 2: Appendix 2 for detailed search terms).\u003c/p\u003e \u003cp\u003eTo identify grey literature and any missed relevant studies, we searched Google to identify any relevant dissertations or non-peer reviewed articles and Google Scholar for any additional relevant papers. We also screened reference lists of relevant systematic reviews investigating similar research questions/topics, and performed backward citation tracing to search the reference lists of included studies.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eEligibility criteria\u003c/h3\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003ePublication date\u003c/h2\u003e \u003cp\u003eWe only included RCTs published from July 2017: the search date of the previous systematic review (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eType of study design\u003c/h3\u003e\n\u003cp\u003eWe only included RCTs of interventions aiming to reduce loneliness and/or improve PSS, as a primary or secondary outcome or one of the main outcomes, as the gold standard for evaluating effectiveness (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e). We included all types of RCTs, including those described by authors as feasibility and pilot studies provided these reported between-group differences; noting the study design and statistical power when reporting findings.\u003c/p\u003e\n\u003ch3\u003ePopulation\u003c/h3\u003e\n\u003cp\u003eWe included trials recruiting people primarily diagnosed with mental health conditions such as depression, post-traumatic stress disorder (PTSD), anxiety, personality disorders, psychosis, and bipolar disorder. Any methods of identifying participants could be used, including clinical diagnosis, validated screening scales, self-report, and use of mental health services. All age groups and geographical locations were included. We excluded trials recruiting participants primarily diagnosed with learning disabilities, autism, dementia or any other organic illnesses, substance use or physical health problems, unless these were comorbid conditions.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eInterventions\u003c/h2\u003e \u003cp\u003eWe included trials that explicitly defined loneliness and/or PSS as the primary outcome or as one of multiple main outcomes of interest or where the interventions evaluated were clearly designed and/or aimed to address loneliness and/or PSS. We excluded studies that defined loneliness and/or PSS as a secondary outcome, without the intervention clearly targeting these factors. We included trials of interventions delivered in person, online or hybrid, and whether individual or/and group.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eComparison\u003c/h3\u003e\n\u003cp\u003eWe included studies with any type of comparison condition, including a waiting list or non-treatment control group or a group that received treatment as usual (TAU) or an active/alternative treatment.\u003c/p\u003e\n\u003ch3\u003eOutcomes\u003c/h3\u003e\n\u003cp\u003eOur primary outcome of interest was subjective social isolation (loneliness or low PSS) assessed using any validated measure. Examples of measures include the UCLA Loneliness Scale (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e) and the Multidimensional Scale of Perceived Social Support (MSPSS) (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e). We excluded studies that only measured objective social isolation (e.g. social network size/received social support). The following secondary outcomes were also examined, if also reported in studies included: i) symptomatic reduction for mental health condition(s) or suicidal ideation/attempt, ii) health status, iii) quality of life, and iv) service use.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eData extraction\u003c/h2\u003e \u003cp\u003eAll search results were exported using Covidence systematic review software (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e) to manage screening. After deduplication, four reviewers (AJ, HG, ZM, IE) independently screened titles and abstracts of retrieved studies against the inclusion criteria. SI independently screened a randomly selected 10% of studies to check consistency of adherence to the criteria. Each full text of potentially eligible studies was screened by one of four reviewers (AJ, HG, IE, JG) and independently screened by one of the two second screeners (SI, ZM). Any disagreements regarding inclusion/exclusion were resolved by group discussion. NM screened the reference lists of relevant systematic reviews investigating similar research questions and conducted the grey literature search. SI conducted backward citation tracing to search the reference lists of studies included in the review.\u003c/p\u003e \u003cp\u003e We agreed on a standardised data extraction table for study characteristics, including: author and publication year, country and study setting, participants\u0026rsquo; characteristics, type of intervention and control group, outcome measures, effectiveness of the intervention (focusing on between group differences and group by time interactions) and risk of bias scores. For each study, one reviewer extracted data, and another reviewer independently checked extracted data for accuracy.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eQuality assessment\u003c/h2\u003e \u003cp\u003eWe used the Cochrane Risk of Bias tool (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e) to assess the quality of included studies. Each study was assessed and rated as having low, some, or high concerns for each of the following domains: sequence generation, allocation concealment, blinding of participants, personnel and outcome assessors, incomplete outcome data, selective outcome reporting, and other sources of bias. Two reviewers (of a team comprising SI, ZM, JG, NM, IE, HG, AJ) independently conducted quality appraisals for each eligible paper, discussing and resolving any discrepancies in any domain.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eData synthesis\u003c/h2\u003e \u003cp\u003eWe conducted a narrative synthesis of findings, based on guidelines from the ESRC\u0026rsquo;s Guidance on the Conduct of Narrative Synthesis in Systematic Reviews (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e). As delineated in our protocol, we divided findings for different conditions and described outcomes for each diagnostic group. Under each mental health category, we summarised important characteristics of the interventions evaluated and trial quality ratings, then described the effectiveness of trials targeting i) loneliness ii) PSS, and iii) other outcomes, contextualising these findings in relation to statistical power (presence/absence of power calculation; adequacy of recruitment).\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eAfter deduplication, we identified a total of 4,321 studies from our searches, of which 174 were eligible for full-text screening. Of these, 40 papers were eligible for inclusion in this review (see Figure 1 for PRISMA flowchart), including one paper that was a secondary analysis (27) of a larger trial that also met inclusion criteria for this review (28). Interrater agreement between reviewers was 90% at title/abstract screening stage and 82% at full-text screening stage, achieving 100% agreement through discussion. \u003c/p\u003e\n\u003cp\u003eA summary of study characteristics including types of samples, sample characteristics, intervention types and summary of findings regarding the effectiveness of the intervention is presented in Tables 1-7 in Additional File 3, grouped by type of mental health condition. Four studies were described as pilot trials (29–32), and two as feasibility studies (33,34), although some of these reported a power calculation. We grouped included papers by the following categories of mental health conditions: depression, post-natal depression (PND), common mental health conditions \u003cem\u003e(\u003c/em\u003e\u003cem\u003edefined as samples that consisted of people with a mixture of depression and anxiety)\u003c/em\u003e, social anxiety disorder, psychosis, post-traumatic stress disorder (PTSD), and mixed samples of people with a range of mental health conditions \u003cem\u003e(\u003c/em\u003e\u003cem\u003edefined as studies among mixed samples of people with a variety of mental health conditions, including those defined as ‘any mental health condition’, or mixed samples consisting of people with a range of conditions, including mood disorders, bipolar disorder, psychotic disorders, anxiety, PTSD)\u003c/em\u003e. Detailed information about study characteristics (including information on descriptive and summary statistics for each study), findings on other outcomes of interest (e.g. service use, symptomatic reduction), and intervention characteristics (e.g. intervention format and duration, detailed description of intervention’ activities and aims, and intervention’s mechanism of change, if reported) is provided in Additional Files 4, and detailed risk of bias scores are presented in Additional File 5. \u003c/p\u003e\n\u003cp\u003eTen studies were judged to have some concerns about bias, and 30 were judged to have high concerns. \u003c/p\u003e\n\u003cp\u003eStudies were conducted in 17 countries including the United States (US; n=14), Australia (n=4), United Kingdom (UK; n=3), Canada (n=2), Turkey (n=2), Spain (n=2), China (n=2), Netherlands (n=2), and Finland, Hong Kong, Iran, Pakistan, Norway, South Korea, Singapore, Malaysia, and Poland (n=1 from each country). A total of 4,474 participants were included, with sample sizes ranging from 18 to 666. Of the 39 interventions evaluated across 40 studies, 14 interventions were group-based, 18 were individual-based, and seven integrated both modalities. Regarding mode of delivery, 23 interventions were conducted face-to-face, 12 interventions were digital, and four were blended (digital and face-to-face). Seven studies focused on adults over the age of 50 (30,35–40), and three focused on young people between the ages of 7-18 (29,41,42). Participants were recruited from a range of settings with most studies recruiting through community settings (e.g. charities, universities, the general population) or primary care services. Nine studies recruited from mental health services, both community and inpatient. Other studies recruited through forensic settings, trauma services, and military services. \u003c/p\u003e\n\u003cp\u003eA range of methods and scales were used to identify mental health conditions; details are shown in Additional file 4. The majority of studies measured loneliness using the UCLA Loneliness Scale. Other measures of loneliness and a range of measures were used to assess PSS across studies included (See Additional File 4: Appendix 4 for measures used in each study). \u003c/p\u003e\n\u003cp\u003eWe also extracted data on our secondary outcomes of interest (e.g. symptomatic reduction for mental health condition(s), health status). A full list of measures used in each study are described in Appendix 5 (See Additional File 4). \u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInterventions for people with depression \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEleven studies focused on people with depression. Studies were conducted in the United States (n=5), and Canada, Hong Kong, Turkey, Iran, and Spain (one from each country). Three interventions were digital interventions, five were face-to-face, and two were blended interventions (face-to-face and digital). Duration of interventions ranged from four weeks to six months.\u003c/p\u003e\n\u003cp\u003eSeven trials measured loneliness and seven trials measured PSS, including three assessing both outcomes (27,28,39). Felton et al. (2019) analysed data from a sub-sample of participants in the trial by Johnson et al. (2019). Sample sizes ranged from 18 to 181 participants with a predominately female range in all studies. One study recruited inpatients (43), two drew on the same sample of incarcerated people(27,28), one recruited from mental health services (30) and the remainder recruited from primary care or community settings. \u003c/p\u003e\n\u003cp\u003eSix studies were judged to have high risk of bias due to methodological concerns, primarily related to outcome measurement (n=4). Other concerns related to: reporting selected findings (n=1), handling of missing data (n=1), and deviation from intended intervention (n=1). \u003c/p\u003e\n\u003cp\u003e\u003cem\u003ea) Loneliness as outcome\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eOf the seven trials in samples with depression, two (one group-based and one individual-based) reported evidence supporting the effectiveness of the intervention. A large statistically significant effect was reported for a community-based group activities intervention even though the study did not achieve the intended sample size (39) and for a fully powered telephone-based individual relational intervention (although this study was a post-hoc analysis of a subset of participants who met criteria for depression) (45). All trials were fully powered, apart from those reported by Joo et al. (2025), which did not achieve the intended sample size, Felton et al. (2019), a subgroup analysis of a larger trial, and Van Orden et al. (2021), a pilot trial that reported a power calculation but did not meet its intended sample size. \u003c/p\u003e\n\u003cp\u003e\u003cem\u003eb) PSS \u003c/em\u003e\u003cem\u003eas outcome\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eSeven trials measured PSS. Moeini et al. (2019) reported that an individual-based online CBT intervention showed evidence of an effect on PSS, although the study did not achieve the sample size required by the power calculation. Conley et al. (2024) also showed evidence of effectiveness for a group-based interpersonal psychotherapy intervention: this was a pilot trial with a sample of only 18 however the difference nonetheless reached statistical significance.\u003c/p\u003e\n\u003cp\u003eFor five trials, the intervention evaluated was not found to be effective. Interventions included an individual solution focused intervention (43), a group spiritual connectivity intervention (46), a mixed (group and individual-based) interpersonal psychotherapy intervention (27,28), and a community-based group activities intervention (39). Two of these trials were fully powered (28,43), two did not meet their target sample size (39,46), and one was a subgroup analysis (27).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e c) Other outcomes of interest\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eOf the 11 trials included in this category of findings, eight trials reported significant reductions in symptoms of depression (27,28,30,32,42–44,46) , and one reported significant improvement in social-emotional quality of life (30). \u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInterventions for women with post-natal depression (PND)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSix trials investigated interventions for women with PND. Studies were conducted in the UK, US, China, Canada, South Korea, and Singapore (n=1 from each country). Five were digital interventions, and one was face-to-face. Duration of interventions ranged from four weeks to three months.\u003c/p\u003e\n\u003cp\u003eTwo trials measured loneliness, and five measured PSS, of which one assessed both (47). Sample sizes ranged from 61 to 150 participants. All recruited from community settings or primary care. \u003c/p\u003e\n\u003cp\u003eFive trials were judged to have high risk of bias, largely due to concerns regarding the handling of missing data and outcome measurement.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003ea) Loneliness as outcome \u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eWe identified two trials that evaluated socially focused programmes, both fully powered. Evidence was reported to support the effectiveness of a group-based online songwriting intervention (48). There was no evidence to support the effectiveness of an individual-based peer support digital intervention (47).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eb) PSS as outcome \u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eOf five trials in this category, one fully powered RCT evaluating a mixed (individual and group-based) digital intervention based on mindfulness and social networking reported evidence to support the effectiveness of the intervention (49). \u003c/p\u003e\n\u003cp\u003eFour trials reported no evidence to support effectiveness of a group-based parenting programme incorporating psychoeducation (33), an individual-based online psychoeducation intervention (50), an individual-based digital CBT intervention (51) or an individual-based digital peer support intervention (47). Two trials included in this category were fully powered (47,51), while Boyd et al. (2017), a feasibility study that reported on differences between the intervention and wait-list condition, did not achieve the intended sample size and Dol et al. (2025), a study that only reported outcomes at six month follow-up was initially fully powered but did not achieve target follow-up rates.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003ec) Other outcomes of interest\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eOf the six trials in PND populations, three trials reported reduction in symptoms of depression (47–49). \u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInterventions for people with common mental health conditions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFive trials focused on groups of people with common mental health problems (a mixture of depression and anxiety). Studies were conducted in Australia, Spain, Poland, Malaysia and China (n=1 from each country). One intervention was digital, another was a blended intervention (face-to-face and digital), and the rest were face-to-face. Duration of interventions ranged from two weeks to four months.\u003c/p\u003e\n\u003cp\u003eFour trials measured loneliness, and one trial measured PSS. Sample sizes ranged from 34 to 133 participants and four studies had a majority of female participants and four recruited individuals over 60 years old. One study recruited from residential care (36) and another via electronic medical records (38), with the rest recruiting from community settings. \u003c/p\u003e\n\u003cp\u003eAll five studies were judged to be at high risk of bias due to methodological concerns, largely related to the outcome measurement (n= 3) and handling of missing data (n=3). Other concerns included potential biases due to: randomisation process (n=1); deviations from intended interventions (n=2); and selective outcome reporting (n=1).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003ea) Loneliness as outcome\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eTwo of four trials with loneliness as an outcome reported evidence of effectiveness. These were a community group-based CBT intervention (40) and an individual and group-based counselling and psychoeducation intervention (37); although both these studies did not report a power calculation and one underrecruited due to COVID-19 restrictions (37).\u003cbr\u003eTwo trials reported no statistically significant differences between intervention and control groups: one evaluating a group-based spiritual reminiscence interpersonal therapy intervention (36) and one an individual-based agent-guided CBT intervention delivered via chat-bot (52). Both these studies exceeded their target sample size but only Syed (2017) based this on a power calculation. \u003c/p\u003e\n\u003cp\u003e\u003cem\u003eb) PSS as outcome\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eA trial with PSS as an outcome reported that a group-based, moderate-intensity physical activity programme was effective, although the intended sample size was not achieved (38). \u003c/p\u003e\n\u003cp\u003e\u003cem\u003ec) Other outcomes of interest \u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eOf the five trials included in this category of findings, three reported significant reductions in symptoms of depression and anxiety (37,38,40). One trial reported a significant improvement in perceived health status (38). \u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInterventions for people with social anxiety disorder\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTwo trials from the U.S focused on social anxiety and measured loneliness as a main outcome (53,54). One was a face-to-face intervention (53) and the other was blended (digital and face-to-face) (54). Duration of interventions ranged from four to twelve weeks and the sample size was 55 to 108 participants. One study included a predominantly female sample (54). One study included recruitment from clinical referrals (53) and the other recruited from community settings (54). \u003c/p\u003e\n\u003cp\u003eBoth studies were judged to have a high risk of bias due to methodological concerns related to the measurement of outcomes.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003ea) Loneliness as outcome\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eOne of the two trials in this category reported that the study intervention was effective. A three-arm trial compared two active group-based interventions (a group-based CBT intervention and a group-based mindfulness-based stress reduction (MBSR) intervention) and a waitlist control group (53). There was no significant difference in loneliness between the CBT and MBSR interventions, but loneliness was significantly lower for both these interventions compared to the waitlist controls. The authors did not report a power calculation. \u003c/p\u003e\n\u003cp\u003eA fully-powered trial evaluating a digital individual-based multi-component intervention targeting fear of intimacy found no evidence of effectiveness (54). \u003c/p\u003e\n\u003cp\u003e\u003cem\u003eb) Other outcomes of interest \u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eNone of the trials of interventions for people with social anxiety disorder reported that interventions were effective for anxiety symptoms.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInterventions for people with psychosis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFour trials focused on people with psychosis. Studies were conducted in the UK, Turkey, Australia and the Netherlands (n=1 from each). All were face-to-face except for one digital intervention (55). Duration of treatment ranged from five weeks to eighteen months.\u003c/p\u003e\n\u003cp\u003eFour trials measured loneliness and two measured both loneliness and PSS (55,56). Sample sizes ranged from 40 to 170 participants. Three studies had samples consisting of approximately equal numbers of males and females and one had a predominately male sample (56). All studies recruited participants with psychosis from mental health services. \u003c/p\u003e\n\u003cp\u003eOne study was rated as having some concern for risk of bias (55), and three trials were judged to be at high risk of bias, mainly due to concerns regarding outcome measurement (n=3) and deviations from intended intervention (n=2). \u003c/p\u003e\n\u003cp\u003e\u003cem\u003ea) Loneliness as outcome\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eOf four included trials, one individual-based intervention evaluating an equine-assisted therapy reported evidence of effectiveness (57). Although this study reported a power calculation, the intended sample size was not achieved. \u003c/p\u003e\n\u003cp\u003eA feasibility study compared Groups for Health (G4H) in its usual group format with individual-based G4H. G4H is a psychological intervention that includes a supported socialisation element and draws on social identity theory. The study found no statistically significant difference between the two G4H conditions; however, this study was intended to test feasibility of a full trial and was not powered to find a significant effect (31). \u003c/p\u003e\n\u003cp\u003eTwo trials found no evidence to support the effectiveness of a mixed (individual and group-based) peer support and online social therapy programme (55) or a mixed (individual and group-based) peer support eating club intervention (56) but both were underpowered with the intended sample size not achieved.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eb) PSS as outcome\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe above trials without evidence of a significant effect on loneliness (55,56) also found no evidence of an effect on PSS. \u003c/p\u003e\n\u003cp\u003e\u003cem\u003ec) Other outcomes of interest\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eOf four trials in this category of findings, one study reported a significant reduction in positive symptoms of psychosis and significant improvement in quality of life (57). \u003c/p\u003e\n\u003cp\u003eOne study assessing use of emergency services reported significantly lower rates of emergency service use in the intervention group compared to the control group (55).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInterventions for people with PTSD\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFour trials focused on people with PTSD. Studies were conducted in the United States (n=2), Pakistan (n=1), and Norway (n=1). All interventions were delivered face-to-face. Two interventions lasted three months and duration was unreported in the other two studies (41,58). Sample sizes ranged from 75 to 162 participants. Two studies recruited predominately male samples of veterans and two studies focused on children. \u003c/p\u003e\n\u003cp\u003eOne study was rated as having some concern for risk of bias (29). Three studies were judged to have high risk of bias due to methodological concerns related to measurement of outcomes (n=2) and potential deviation from the intended intervention (n=1). \u003c/p\u003e\n\u003cp\u003e\u003cem\u003ea) PSS as an outcome \u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eAll four trials in this category focused on PSS rather than loneliness. An RCT of an individual-based prolonged exposure therapy intervention (59) and another pilot trial of a group-based CBT intervention reported the intervention to be effective (29); despite each having small samples and no power calculation.\u003c/p\u003e\n\u003cp\u003eThere was no significant evidence of effect for an individual-based trauma-focused CBT intervention (41) or for an individual-based behavioural activation psychotherapy intervention (58), but both were underpowered. \u003c/p\u003e\n\u003cp\u003e\u003cem\u003eb) Other outcomes of interest \u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eOf the four trials included in this category of findings, three studies reported evidence of a significant reduction in symptoms of PTSD (41,59) of which one was a small pilot trial (29).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInterventions for mixed samples of people with a variety of mental health conditions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEight trials recruited samples of people with a variety of mental health conditions. Studies were conducted in the US (n=3), the UK (n=1), Australia (n=2), Finland (n=1) and the Netherlands (n=1). Two interventions were digital, and the rest were face-to-face. Duration of interventions ranged from a single session to three years.\u003c/p\u003e\n\u003cp\u003eSeven trials measured loneliness and two trials measured PSS, including one trial which measured both (60). Sample sizes ranged from 40 to 335 participants. The majority of studies (n=6) had samples consisting of 60% or more female participants. Two studies recruited participants from community settings (61,62), and others from health service settings (34,63–65).\u003c/p\u003e\n\u003cp\u003eTwo studies were judged to have some concerns about bias, whilst six studies were judged to be at high risk of bias, mainly due to methods for measuring outcomes (n=6), missing outcomes (n=4), randomisation process (n=1), or selective outcome reporting (n=1).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003ea) Loneliness as outcome \u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eOne of the seven studies with mixed samples reported evidence of effectiveness. A fully powered trial evaluating the effectiveness of the Groups 4 Health (G4H) intervention reported a significant reduction in loneliness in the G4H group compared to treatment as usual (62). \u003c/p\u003e\n\u003cp\u003eA feasibility trial of an individual and group-based peer-delivered supported socialisation intervention (Community Navigators) found no statistically significant difference in outcomes between an experimental group receiving the intervention and a treatment as usual control, but this trial was primarily conducted to test feasibility of conducting a full trial and was not powered to detect a difference (34). An individual-based intervention combining psychoeducation and cognitive bias modification showed significant reductions in thwarted belongingness in the intervention group compared to treatment as usual; however this study was a post-hoc exploratory sub-analysis of a small subgroup of a larger trial and was underpowered (66). \u003c/p\u003e\n\u003cp\u003eFour trials found no evidence to support the effectiveness of an individual-based caring-contact intervention (63), an individual and group-based peer-delivered community participation programme (64), the Groups 4 Health intervention (61) or an individual-based social skills support and supported socialisation programme (60). Two of these trials were fully powered (61,63), while one (64) did not report a power calculation, and one (60) did not achieve its target sample size and reported high dropout rates.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eb) PSS as outcome \u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eTwo trials measured PSS. There was no evidence of any difference in effectiveness between a long-term individual-based psychodynamic psychotherapy intervention, short-term psychodynamic therapy and short-term solution focused therapy in a three-arm trial (65) or between a supported socialisation programme and control group (60). One study did not achieve its target sample size (60) and the other study did not report a power calculation but reported achieving a large sample size (65). \u003c/p\u003e\n\u003cp\u003e\u003cem\u003ec) Other outcomes of interest \u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eOf the eight trials conducted with mixed samples, one trial reported that the intervention evaluated led to significant improvements in symptoms of social anxiety (62) and one reported a small but significant decrease in suicidal ideation (63). Two studies reported a decrease in service use and duration of psychiatric admission (60,62). \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eOur findings suggest that, based on trials published from 2017\u0026ndash;2025, some psychologically-focused interventions (including cognitive behavioural/modification approaches and mindfulness-based interventions), and some supported socialisation/socially focused interventions delivered in group settings are effective at reducing loneliness and/or improving PSS. Recruitment in these studies was from a wide range of settings, including community settings, primary care and mental health services. Of the 40 studies of 39 interventions included in this review of recent trials, 15 studies (evaluating 16 types of interventions) reported significant improvements in PSS and/or loneliness. These interventions included: five involving supported socialisation/socially focused interventions (e.g. support in engaging in social activities)(\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e) (one of which was based on a psychological theory of loneliness: social identity theory (\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e)), five CBT interventions (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e, \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e), and one of each of the following: a mixed intervention integrating a social networking component and mindfulness techniques (\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e), an intervention combining individual counselling and group psychoeducational sessions (\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e), a MBSR intervention (\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e), prolonged exposure therapy (\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e), interpersonal psychotherapy (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e), and equine-assisted therapy(\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e) (See Additional File 4 Appendix 6 for characteristics of interventions evaluated in this review). One trial of a community-based group activities interventions reported positive effects of the intervention for loneliness but not PSS among people with depression (\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eRegarding negative findings, of the 40 included studies, a total of 9 fully powered trials (evaluating 10 types of interventions) reported no group differences in PSS and/or loneliness. These interventions were: i) six types of psychological interventions including an interpersonal psychotherapy intervention (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e), a behavioural activation intervention (\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e), a solution focused intervention (\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e), a CBT intervention (\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e), a spiritual reminiscence interpersonal therapy intervention (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e), and a multi-component intervention targeting fear of intimacy (\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e), and ii) three interventions involving supported socialisation/socially focused or relational or individual peer support approaches (See Additional File 4 Appendix 6 for characteristics of interventions evaluated in this review).\u003c/p\u003e \u003cp\u003eA total of 12 underpowered trials and one pilot and two feasibility studies reported negative findings of which six were supported socialisation/socially focused interventions (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e, \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e, \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e) and nine were psychologically focused interventions (\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e, \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e, \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e). As these findings were based on underpowered trials, we cannot draw any clear conclusions regarding the effectiveness of these interventions.\u003c/p\u003e \u003cp\u003eMost studies recruited from the general population or primary care. Only nine studies recruited participants from mental health services, and of these, only one reported positive results for an equine-assisted intervention for people with psychosis (\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAlthough we sought to identify types of interventions that might be effective for people with specific mental health conditions (e.g. depression, PTSD), no clear pattern emerged regarding which types of interventions work best for specific clinical groups. Furthermore, the interventions, their intended mechanisms of action (See Additional File 4) and target populations varied greatly between studies. We therefore decided that neither meta-analysis nor GRADE ratings of confidence in findings were appropriate. Overall, this heterogeneity between studies, the low methodological quality of many included studies, and predominance of underpowered trials (including pilot studies) restricted our ability to draw robust and clear conclusions regarding which types of interventions are most effective in the context of different types of mental health conditions.\u003c/p\u003e \u003cp\u003eComparing the findings of the previous review (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e) (covering the 19 eligible trials published until 2017 that focused on subjective social isolation) and our review (covering the 40 eligible trials published from 2017\u0026ndash;2025), both draw similar conclusions. This was despite the proliferation of trial publications over the more recent period, and the assumption that trial methods might have improved over that time. Both reviews conclude that it is not possible to determine the most effective treatment approaches from the evidence included in each synthesis, nor what may work best for different clinical groups. However, our review of more recent literature did, in contrast to the previous review, identify a number of social and psychosocial interventions with some evidence of effectiveness. In most cases, each intervention was supported by only one trial, with trials often of limited quality and scale. We therefore view these trials as a starting point for further work, including good quality replication studies, to test and establish whether these interventions are ready for wider implementation. Several social interventions (primarily tested in underpowered trials) were ineffective, and the reasons for this remain unclear, although this is likely attributable to the lack of fully powered trails evaluating these interventions.\u003c/p\u003e \u003cp\u003ePeople with mental health conditions experience difficulties in forming and maintaining social connections resulting from a range of societal barriers (e.g. social exclusion) (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e). Mechanistically, socially focused interventions may offer individuals opportunities to engage in social groups/activities and develop positive social connections and group membership that then reduce feelings of loneliness and promote a sense of belonging and social inclusion (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e). Our provision of further detail about intervention descriptions, components/activities, and characteristics (see Additional file 4: Appendix 6) will provide those engaged in theory of change and/or intervention development with further clues as to likely pathways.\u003c/p\u003e \u003cp\u003eOur review also identified some recent evidence supporting the effectiveness of cognitive behavioural approaches for addressing loneliness and/or PSS. This is supported by preliminary findings from a previous systematic review and a narrative review focused on people with mental health conditions (covering studies published since inception), which suggested that interventions focused on addressing and changing maladaptive social cognitions are effective at reducing subjective social isolation in people with mental health conditions (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e). For psychological interventions in general, we identified a small number (n\u0026thinsp;=\u0026thinsp;4) of recent studies reporting the effectiveness of psychologically-based interventions such as mindfulness-based approaches (\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e, \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e). However, negative findings were reported for several psychological interventions evaluated in nine underpowered trials and six fully-powered trials.\u003c/p\u003e \u003cp\u003eIt is also worth noting that some recently published studies in our review reported improvement in mental health outcomes but no positive effects on PSS and loneliness (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e). This might indicate that loneliness and PSS are difficult to shift even when interventions successfully improve other outcomes.\u003c/p\u003e \u003cp\u003eOverall, our synthesis of recent evidence, primarily based on underpowered trials, identified a range of social and psychological interventions that may be effective at reducing loneliness and improving perceived social support; serving as a basis for further work to test their effectiveness in diverse settings and clinical groups, using adequately powered trials. Negative findings were reported for several interventions and interventions widely varied thereby making it difficult to identify conclusive patterns regarding what types of interventional approach are most effective.\u003c/p\u003e\n\u003ch3\u003eStrengths and limitations\u003c/h3\u003e\n\u003cp\u003e We conducted a systematic review of studies published after July 2017, adhering to the PRISMA guidelines, synthesising the recent evidence on the effectiveness of interventions aiming to reduce subjective social isolation among people with different mental health conditions, focusing on RCTs as the gold standard for testing effectiveness. However, there are a number of limitations to consider in interpreting our findings. We decided to only include trials that focused on subjective social isolation as a primary/one of the main outcomes and where the interventions evaluated clearly focused on reducing subjective social isolation. This meant that we excluded interventional trials that were not designed to clearly target subjective social isolation, even if they did provide evidence of effectiveness in reducing it. Furthermore, the heterogeneity of included studies regarding types of interventions, study participants, and settings led to our reliance on a narrative synthesis approach and meant that meta-analysis was inappropriate. Moreover, some of the studies reporting significant effects had small sample sizes and were underpowered, raising the possibility of Type 1 errors (\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e). Finally, this review only focused on studies conducted from July 2017 onwards, which meant that our synthesis did not include earlier research findings.\u003c/p\u003e\n\u003ch3\u003eResearch and clinical implications\u003c/h3\u003e\n\u003cp\u003eThe main implications that can be drawn from these findings for policymakers relate to policies for people with mild/moderate psychiatric symptoms primarily recruited from community settings/services, educational settings, and primary health care services; the samples used in the majority of studies. Based on our findings for these groups, there are grounds for further testing social interventions and psychological interventions such as CBT focused on addressing subjective social isolation, delivered in group settings. Where interventions included in our review show evidence of some effectiveness, larger-scale studies that are fully powered and of high quality would be helpful to understand whether they are indeed effective. These studies would benefit from also evaluating whether these interventions have an impact on mental health outcomes/symptoms and overall quality of life. Importantly, an important evidence gap remains for people with more severe mental health illness, such as psychosis, and secondary mental health service users for which there were few good quality trials, and for whom we know the experience of loneliness to be debilitating (\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e). Future research should address the quality issues in such trials complemented by studies to explore acceptable approaches, particularly for co-developed interventions tailored to the specific social needs of people with different mental health conditions. Future refinements of such interventions should be informed by a clearly defined theory of change, evaluated for acceptability, and trialled using adequately powered and rigorously designed RCTs.\u003c/p\u003e \u003cp\u003eOur findings, based on recent evidence, indicate that both social and psychological interventions may have potential to reduce subjective social isolation, as well as interventions that may be hybrids of both approaches, such as Groups 4 Health. In other populations including the general population, a wide range of psychological and social interventions have also been trialled, with a recent umbrella review suggesting that psychological interventions may be more effective for loneliness, although with positive reports also for some mixed interventions (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e). Little work so far allows conclusions to be drawn about what works best for whom, and it may be that, as suggested by Eager et al.\u0026rsquo;s (2024) qualitative findings, psychological strategies are more suitable for long-term loneliness and social strategies for transient and situational loneliness (\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e). In further research, attention should be given to developing theoretically informed interventions with clear pathways, incorporating input from people with relevant lived experience, and informed by the increasing body of evidence on potential causes of loneliness among people with mental health conditions; all of which would help in developing effective interventions (\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e). In planning and conducting these trials, it is important to address common methodological issues that impact the rigor and credibility of findings, noted in our review, such as a neglect of power considerations. Strategies are also needed to minimise high attrition rates (particularly in the event of future pandemics) and handle missing outcomes.\u003c/p\u003e \u003cp\u003ePending further evaluations and adaptations of interventions identified as potentially effective in this review and more definitive trial evidence, and given that connectedness is a highly valued recovery outcome among people with mental health conditions (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e), it is important for mental health practitioners to ask about subjective social isolation in practice and consider patient-centered means of addressing this. There may also be practice insights and pointers/directions for further intervention development to be gained from trials focused on general population samples. For instance, there is systematic review evidence to support the effectiveness of CBT, mindfulness-based interventions, and interventions based on social identity theory; with the most consistent evidence supporting the use of CBT (\u003cspan additionalcitationids=\"CR73\" citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e).\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003e Our comprehensive systematic review of recent trials (published from 2017\u0026ndash;2025) identified 40 studies evaluating interventions aimed at reducing subjective social isolation among people with mental health conditions. Our synthesis provided preliminary evidence to suggest that interventions involving supported socialisation and social group activities and psychological interventions such as cognitive behavioural therapy addressing maladaptive social cognitions may be effective in alleviating subjective social isolation in some contexts and clinical groups, but firm conclusions rely on replicability and higher quality studies. The low methodological quality of these trials and lack of well-powered trials therefore limited our ability to make definitive conclusions and specific recommendations for practice. Despite our efforts to identify which types of interventions are most effective for different types of mental health conditions, the lack of robust evidence meant that we could not determine from this recent evidence which interventions and interventional components are most effective for different clinical groups particularly for people with severe mental health conditions. Future research should develop theoretically-driven and acceptable interventions targeting subjective social isolation tailored to the social needs of people with specific psychiatric diagnoses and evaluate their effectiveness using fully-powered and rigorously designed RCTs.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eCBT: Cognitive Behavioural Therapy\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMBSR: Mindfulness-Based Stress Reduction\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eN: Number of participants\u003c/p\u003e\n\u003cp\u003ePND: Post-Natal Depression\u003c/p\u003e\n\u003cp\u003ePRISMA: Preferred Reporting Items for Systematic Reviews and Meta-Analyses\u003c/p\u003e\n\u003cp\u003ePTSD: Post Traumatic Stress Disorder\u003c/p\u003e\n\u003cp\u003ePSS: Perceived Social Support\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eRCT: Randomised Controlled Trial\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTAU: Treatment As Usual\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eUK: University Kingdon\u003c/p\u003e\n\u003cp\u003eUS: United States\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eUCLA: University of California, Los Angeles\u0026nbsp;\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate: \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot Applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publications: \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot Applicable \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials: \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data analysed during this study are included in this published article and its supplementary information files.\u0026nbsp;No new datasets were generated. Therefore, data sharing is not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests: \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding: \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe acknowledge salary support for SI, AP, BLE, and SJ from the National Institute for Health and Care Research (NIHR) University College Hospitals London (UCLH) Biomedical Research Centre (BRC) for funding the activities of the Loneliness and Social Isolation in Mental Health Research Network.\u003c/p\u003e\n\u003cp\u003eThis funding source had no direct involvement in the review design, analysis, decision to publish or preparation and submission of the manuscript.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; contributions: \u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSI, BLE, AP, and SJ collaboratively developed the research protocol. AJ, HG, ZM, and IE screened titles and abstracts of all potentially relevant papers identified from the databases. SI independently screened the titles and abstracts of randomly selected 10% of papers. The full texts were independently co-screened by one of four reviewers (AJ, HG, IE, JG) paired with one of two co-screeners (SI, ZM). For each study, one reviewer extracted data, and another reviewer independently checked the extracted data for accuracy (AJ, HG, IE, JG, NM, ZM, SI). Two reviewers (of a team comprising SI, ZM, JG, NM, IE, HG, AJ) independently conducted quality appraisals for each eligible paper in pairs.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;NM screened the reference lists of relevant systematic reviews investigating similar research questions and conducted the grey literature search. SI conducted\u0026nbsp;backward citation tracing to search the reference lists of studies included in the review.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;SI, NM, JG, and AJ wrote the manuscript. AP, BLE, and SJ reviewed the manuscript. All authors approved the final manuscript.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments: \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eWang J, Lloyd-Evans B, Giacco D, Forsyth R, Nebo C, Mann F, Johnson S. Social isolation in mental health: a conceptual and methodological review. Soc Psychiatry Psychiatr Epidemiol. 2017;52(12):1451\u0026ndash;61.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSantini ZI, Jose PE, Cornwell EY, Koyanagi A, Nielsen L, Hinrichsen C, Meilstrup C, Madsen KR, Koushede V. 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BMC Public Health. 2023;23(1):2214.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBirken M, Ikhtabi S, Steare T, Johnson S, Benedetto G, Lin F, Scott HR, Harju-Sepp\u0026auml;nen J, McCloud T, Shafran R, Pitman A. Investigating the effectiveness of interventions intended to reduce loneliness using psychological strategies and a theory of change: a systematic review of interventional studies and meta-analysis. BMC Psychol. 2025;14:131.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJarvis MA, Padmanabhanunni A, Balakrishna Y, Chipps J. The effectiveness of interventions addressing loneliness in older persons: an umbrella review. Int J Afr Nurs Sci. 2020;12:100177.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-medicine","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmed","sideBox":"Learn more about [BMC Medicine](http://bmcmedicine.biomedcentral.com/)","snPcode":"12916","submissionUrl":"https://submission.nature.com/new-submission/12916/3","title":"BMC Medicine","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Subjective social isolation, mental health, loneliness, perceived social support, systematic review, randomised controlled trial, trial","lastPublishedDoi":"10.21203/rs.3.rs-9576879/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9576879/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eSubjective social isolation (loneliness and/or low perceived social support; PSS) is prevalent among people with mental health conditions and developing interventions to alleviate it is a priority. This systematic review provides an up-to-date synthesis of the recent evidence on the effectiveness of interventions aimed at alleviating subjective social isolation among people with mental health conditions.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eWe searched three electronic databases (Medline; PsycINFO; Web of Science) from July 2017 (the date of our group\u0026rsquo;s previous last review on this topic) to May 2025 for randomised controlled trials evaluating the effectiveness of any type of intervention that targeted subjective social isolation among people with any mental health condition. We conducted quality appraisals using the Cochrane Risk of Bias tool and used a narrative synthesis approach to summarise findings.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eA total of 40 papers, describing 39 trials including 4,474 participants, met eligibility criteria. Findings were grouped by type of mental health condition. Fifteen trials evaluating 16 types of interventions found evidence supporting the effectiveness of specific interventions: five socially-focused approaches, five cognitive behavoural therapy interventions, and six other interventions (including mindfulness-based interventions and equine-assisted therapy). Many included studies appeared to have low power or were pilot or feasibility studies. The majority of studies focused on people with common mental health conditions and recruited from community settings or through primary care services.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eOur synthesis of recent literature demonstrates that some psychological approaches (such as cognitive behavioural therapy) and social interventions delivered in group settings show evidence of effectiveness in reducing subjective social isolation. Despite methodological limitations and the predominance of underpowered trials, this body of work has potential to inform further development and testing, ideally through adequately powered trials, of interventions designed to reduce loneliness and improve perceived social support among people with mental health conditions.\u003c/p\u003e","manuscriptTitle":"The effectiveness of interventions for reducing loneliness and improving perceived social support among people with mental health problems: A systematic review of recent literature","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-15 02:37:14","doi":"10.21203/rs.3.rs-9576879/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewersInvited","content":"","date":"2026-05-06T07:13:16+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-05-05T17:29:46+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-05-01T09:29:09+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-05-01T08:48:22+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Medicine","date":"2026-04-30T11:46:59+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-medicine","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmed","sideBox":"Learn more about [BMC Medicine](http://bmcmedicine.biomedcentral.com/)","snPcode":"12916","submissionUrl":"https://submission.nature.com/new-submission/12916/3","title":"BMC Medicine","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"c4e714a8-f9cc-45fb-bc77-0d47c61b5351","owner":[],"postedDate":"May 15th, 2026","published":true,"recentEditorialEvents":[{"type":"reviewersInvited","content":"12","date":"2026-05-06T07:13:16+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-05-05T17:29:46+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-05-01T09:29:09+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-05-01T08:48:22+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Medicine","date":"2026-04-30T11:46:59+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-15T02:37:14+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-15 02:37:14","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9576879","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9576879","identity":"rs-9576879","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}