Substance abuse and academic performance among university students: systematic review and meta-analysis

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Substance abuse is a widespread concern among young adults and is particularly significant among college students. Substance abuse in this population is linked to numerous academic, physical, mental, and social difficulties. This systematic review and metanalysis explores whether there is an effect of the illegal drug and alcohol consumption behaviors on academic achievement among university students. Methods. The databases searched were MEDLINE, CINHAL, Scopus, ERIC, and PROSPERO, updated in January 2025. The risk of bias was assessed using the Edward score. We used a random-effects model. The protocol of this review was registered in the Open Science Framework. Results. The systematic review included 21 studies, while the meta-analysis included four studies. In a sample of 1,219 subjects in the control group and 350 illegal drug consumers, there is a negative and significant effect of drug consumption on academic achievement [SMD = − 0.61 (95% CI − 0.84 to − 0.38; p = 0.008). In a subgroup analysis, a sample of 2,479 subjects in the control group and 7,134 alcohol consumers, there is a small effect of alcohol consumption on academic achievement [SMD = − 0.24 (95% CI -0.51 to 0.04; p = 0.073). Conclusions. This systematic review provides quantitative evidence on the relationship between legal and illegal use of drugs among university students and academic achievement. Specifically, we found a significant medium effect of substance abuse in general and a small effect for alcohol consumption on academic achievement. alcohol drinking drug use disorders university student academic achievement Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Substance abuse is a widespread concern among young adults [ 1 – 3 ] and is particularly significant among college students. University students represent a high-risk group for both legal and illegal drug use, as this academic period often marks their first experience with reduced parental oversight [ 4 ] and introduces stressors related to new relationships and the challenges of successful adaptation [ 5 ]. Substance abuse in this population is linked to numerous academic, physical, mental, and social difficulties. Research indicates that nearly half of college students meet the criteria for at least one substance use disorder (SUD), and young adults aged 19–30 report elevated rates of cannabis use, vaping (both cannabis and nicotine), and hallucinogen use [ 6 , 7 ]. This issue presents serious public health implications, contributing to increased rates of morbidity and mortality [ 1 – 3 ]. Specifically, alcohol abuse is associated with mental disorders [ 8 , 9 ], highly disabling outcomes [ 10 ], and physical and psychiatric comorbidities [ 11 ]. Some studies have shown that excessive alcohol consumption and substance use are associated with difficulties in adapting to academic life, poor working memory and reasoning [ 12 ], lower intelligence, and reduced attention in both adolescents and college students [ 13 ]. In addition, other consequences are decreased academic performance [ 14 , 15 ], less time studying, disengagement from academic duties [ 16 ], and increased academic procrastination [ 17 ]. High levels of academic failure are a great problem for universities' reputation because they can lose potential new students [ 18 , 19 ]. Contrasting academic failure means also promoting human development and increasing the social and cultural capital of the country, creating the conditions for economic development and the progress of society [ 20 ]. In addition, students generally do not use only one drug but more substances together [ 21 ], and these associations can further aggravate the negative consequences of academic failure of university students. Consumption of legal and illegal drugs among university students In Western countries, the consumption of legal and illegal drugs has increased in recent years among the university population [ 22 ]. In the United States, among college students and young people, the frequency of binge drinking (consuming four/five or more drinks for women/men) and substance use is high (30–40%) [ 23 , 24 ]. In Finland, 22% of college students smoke, 21% use illicit drugs, 41% are high-frequency drinkers, and 31.4%, 16.3%, and 6.7% show one, two, or three abuse-associated behaviours (alcohol, tobacco, and other drugs), respectively [ 25 ]. Consumption of tobacco, alcohol, and illegal drugs like cannabis is prevalent among Spanish university students [ 26 , 27 ], and alcohol use is common in 18–24-year-old people who reported the habit of drinking, binge drinking [ 28 ]. Fadhel [ 29 ] assessed substance abuse among university students in Yemen and Saudi Arabia and found that 12.5% of students use sedative drugs, and the overall prevalence of drug abuse was low (27.2%), moderate (10.5%), substantial (2.1%) and severe (0.8%). In Egypt, Kabbash et al., [ 30 ] found that university students use cigarettes (8.9%), tranquilisers (4.3%), hashish (3.6%), alcohol (2.7%), bhang (1.4%), and tramadol (1.0%). In Africa, among Tunisian university students, the prevalence of high-risk alcohol consumption and alcoholic disorder is 52.5% and 79.1%, respectively [ 31 ], and in Ethiopia, the prevalence of alcohol consumption is 35.5% [ 32 ]. Numerous studies have investigated the association between academic achievement and the use of legal or illegal substances among university students. While some research indicates that substance abuse and alcohol consumption negatively impact academic performance [ 33 ], other studies have found no significant relationship between these variables [ 34 , 35 ]. This study aims to systematically review quantitative literature exploring the relationship between legal and illegal drug use among university students and academic achievement. Specifically, it seeks to determine whether drug consumption behavior has an effect on academic performance. Methods A systematic literature review and meta-analysis was conducted. The PRISMA guidelines guided the processes of source selection, data extraction, and data presentation [ 36 ]. This review protocol was registered in the Open Science Framework. Eligibility criteria We formulate a research question based on the PICO method: Population (university student), Intervention (legal or illegal drug use), Comparison (no substance abuse), and Outcome (academic achievement). For the topic, we decided on the following inclusion criteria: any empirical quantitative study design regarding university students’ substance abuse (alcohol, tobacco, cannabis, and other legal and illegal drugs) and academic achievement in peer-reviewed journals in every language. Exclusion criteria are empirical studies regarding substance abuse and academic achievement in non-university students, articles without full text available, conferences, editorials, theses and books, case reports, case series, and systematic review studies. No data frame was considered. Information sources The literature search was developed based on medical subject headings (MeSH), keywords, and free-text words related to university students, alcohol abuse, and academic achievement. We performed the search in electronic databases, including MEDLINE, CINHAL, Scopus, and ERIC. In addition, in PROSPERO, updated in January 2025. We researched ongoing or recently completed systematic reviews. Search strategy The mesh terms, keywords, and free-text words used in the search strategy were combined with the Boolean operator “AND”/“OR ” (“Students”, OR “School enrolment”, OR “Universities”) AND (Alcohol-Induced Disorders”, OR “Alcohol drinking”, OR “Binge Drinking”, OR “Abuse, Marijuana”, OR “Hashish Abuse”, OR “Cannabis Abuse”, OR “Substance-Related Disorders”, OR “Cannabis Related Disorders”, OR “Drug Use Disorders”, OR “Substance Abuse”, OR “Substance Addiction”, OR “Drug Dependence”) AND (Academic success”, OR “Academic achievement”, OR Academic performance”, OR “Academic test score”) (Additional file 1). Selection process Three researchers (I. S., R. M., G. B.) independently examined the studies based on the title and abstract. All records obtained from the literature search were collected into the Endnote library to delete duplicates. In this phase, the researchers decided the studies to include based on eligibility criteria (empirical studies, concerning university students, evaluating substance abuse and academic achievement, written in all languages). We scanned the references of all included studies. The studies were excluded for lack of precision of the research question, a different population from that of interest (adolescent, primary and secondary students), and academic success not measured quantitatively. Academic achievement was defined as the performance obtained in the programme by the student as the grade point average in every situation (course, cumulative GPA at the end of the year and from one year to another). Substance abuse was defined as all substances (legal or illegal drug) assumed by the university student. When there was a doubt about including a study, the study was included for discussion in the final decision with the agreement of everyone. In case of disagreement among researchers, a senior researcher’s intervention was considered. When some study was excluded, the reasons were declared. We also performed a manual search analysing the references from the included studies. Each step performed independently was discussed for agreement in the large group of researchers. Data collection process All data extracted were collected in an Excel sheet. Three researchers (I. S., R. M., G. B.) extracted data independently, and, in case of disagreement, reviewers resolved it by discussion. We contacted the study authors to resolve any doubt. Data items We collected the following data from each study: author name, year of publication, country, aim of the study, study design, overall sample size, demographic characteristics, instrument used to measure the substance use, instrument to measure the academic achievement, the number of students with substance abuse (any definition: only alcohol use, alcohol + any drug use, binge drinking, etc.), the number of students without substance abuse. In case of a longitudinal study, we collected the time at which the analysis was performed. When a study consisted of multiple groups, such as a different group based on drug consumption frequency, we combined the groups to have only one group of student drug consumers. We collected data on the quantitative modality of the assessment of academic achievement and we considered the average, standard deviation, standard error (SE), median, range, and interquartile range of academic success in students not consuming drugs and those consuming drugs. If effect sizes cannot be calculated, we contacted the authors for additional data. Outcomes and prioritisation The primary outcome was the effect of substance abuse on academic achievement. Risk of bias assessment The risk of bias was assessed using the Edward score [ 37 ] for observational studies. The 11 items of the assessment tool are as follows: definition of aims, sample formation, description of inclusion and exclusion criteria, description of subject characteristics, power calculation, objectivity of outcome measures used, adequacy of follow-up, adequacy of analysis (intention to treat), adjustment for baseline differences between groups, appropriate unit of allocation to groups, and randomisation method. Each item is scored from 0 to 2 for adequacy, and a high score indicates a study’s high methodological quality. The total score possible ranges from 0 to 22 for experimental studies and from 0 to 16 for observational studies. Effect measures The standardized mean difference (SMD) was chosen as summary statistic to synthesize the effect of drug consumption behaviour on academic achievement. Data synthesis If the studies are sufficiently homogeneous in terms of drug consumption definition and sample population, we conducted meta-analyses using a random-effects model. Meta-analysis was the statistical technique used to synthesise results when mean and standard deviation (SD) of academic achievement in drug/alcohol consumers group and in non-consumers group were available. A random-effects mode was performed, with DerSimonian and Laird estimation of the between-study variance. A forest plot was used to represent the meta-analysis results. The heterogeneity between the studies was assessed by visual inspection of the forest plot and by the overlap of the CIs and possible outliers, and it was quantified through the I 2 index. The I² statistic describes the percentage of variation across studies that is due to heterogeneity rather than chance. We considered that an I 2 of 25% indicated low heterogeneity, 50% moderate, and 75% high [ 38 ]. A p value of the chi-squared (χ2) test, a statistical test for heterogeneity, was included in the forest plot. A possible source of heterogeneity (e.g., mean age) was not investigated by meta-regression since there are fewer than 10 studies [ 39 ]. Publication bias was assessed with visual inspection of the funnel plot, that is, a scatter plot of the effect estimates from individual studies against SE. The funnel plot asymmetry was not verified due to the small number of studies included in the meta-analysis. Results Study selection We combined the three search strings (1#2#3), retrieving a total of 1,477 records. After removing 48 duplicates, 1,429 unique records remained. The last search was conducted in January 2025. After screening titles and abstracts, 1,370 records were excluded as they were not relevant to our research aims. The remaining 59 studies underwent full-text evaluation. Of these, 38 studies were excluded for the following reasons: they did not focus on academic achievement (n = 11), were not empirical studies (n = 8), did not consider university students (n = 8), did not quantify academic success (n = 4), or were reviews (n = 7). As a result, 21 studies were included in the final selection (Fig. 1 ), of which four were deemed suitable for meta-analysis. Study characteristics We included 21 studies (Additional file 2). The time frame for publication is from 2007 to 2023. The countries more represented were the USA with eight studies [ 15 , 41 – 47 ], Spain with three studies [ 35 , 48 , 49 ], the United Kingdom with two studies [ 50 , 51 ], and one study each in Qatar [ 34 ], Ethiopia [ 52 ], Nigeria [ 53 ], Brasil [ 54 ], Romania [ 55 ], Hungary [ 56 ], Lithuania [ 57 ] and Australia [ 33 ]. The studies considered different types of university students coming from different courses, public or private universities, and different sample sizes, with a minimum of 129 students [ 49 ] and a maximum of 23,518 [ 47 ]. The consumption of legal or illegal drugs was measured with different instruments, and different substances were considered with single or aggregate data. An et al. [ 15 ], El Ansari et al. [ 34 ], El Ansari et al. [ 50 ], Liguori and Lonbaken [ 43 ], Mercado et al. [ 45 ], Nasui et al. [ 55 ], Pascarella et al. [ 46 ], Piazza-Gardner et al. [ 47 ], and Tembo et al. [ 51 ] evaluated only alcohol consumption. An et al. [ 15 ], El Ansari et al. [ 50 ], Liguori and Lonbaken [ 43 ], Pascarella et al. [ 46 ], and Piazza-Gardner et al. [ 47 ] classify the level of abuse behaviours with one or more items. El Ansari et al. [ 34 ] use the CAGE [ 58 ]; Mercado et al. [ 45 ] use the Short Alcohol Dependence Data Questionnaire (SADD) Raistrick et al. [ 59 ]; [ 49 ] use AUDIT [ 60 ]; Tembo et al. [ 51 ] use the AUDIT [ 61 , 62 ]; and Nasui et al. [ 55 ] use the Romanian version of the Student Alcohol Questionnaire [ 63 ]. Ache Akua and Samek [ 41 ] evaluate alcohol and cannabis consumption with two items. Olorunleke et al. [ 53 ] considered alcohol and tabacco and evaluated them with a structured questionnaire. Petkeviciene et al. [ 57 ] considered alcohol, drug use (ecstasy, cocaine, LSD, cannabis,…) and smoking and evaluated them with a questionnaire for drung and smoking, while used the CAGE questionnaire for alcohol abuse and dependence [ 58 ]. Arria et al. [ 42 ], Hernandez-Serrano et al. [ 35 ], Lukacs et al. [ 56 ], Meda et al. [ 44 ], Mekonen et al. [ 52 ], Ong et al. [ 33 ], Paramo et al. [ 48 ], and de Souza et al. [ 54 ] assess more than one drug use. Arria et al. [ 42 ] evaluates alcohol and marijuana, inhalants, heroin, cocaine, hallucinogens, amphetamine/methamphetamine, and ecstasy consumption. For alcohol dependence, Arria et al. [ 42 ] use the DSM-IV criteria based on the questionnaire from the Substance Abuse and Mental Health Services Administration [ 64 ], while they use some questions for the other substances. de Souza et al. [ 54 ] assess alcohol, marijuana, and cocaine use with the Alcohol, Smoking, and Substance Involvement Screening Test (ASSIST) [ 65 ]. Hernandez-Serrano et al. [ 35 ] assess alcohol, cannabis and tobacco use; Lukacs et al. [ 56 ] assess alcohol, tobacco, ecstasy, depressant, and herbal drug use; Meda et al. [ 44 ] assesses alcohol and marijuana use; and Mekonen et al. [ 52 ] assess alcohol, smoking, and other substances with the ASSIST [ 65 ]. Ong et al. [ 33 ] assess alcohol and smoking use with the NSW questionnaire [ 66 ], and Paramo et al. [ 48 ] assess alcohol use with the AUDIT-C [ 61 , 67 ] and cannabis use with the CAST [ 68 , 69 ]. Academic achievement was assessed with self-reported data [ 15 , 33 – 35 , 41 , 42 , 45 – 47 , 49 – 57 ] or by administrative database [ 43 , 44 , 48 ]. Meda et al. [ 44 ] and Paramo et al. [ 48 ] use the GPA, while Liguori and Lonbaken [ 43 ] use the first–second year retention. For self-reported data, An et al. [ 15 ], Mekonen et al. [ 52 ], and Piazza-Gardner et al. [ 47 ] used the GPA with a range from 1 to 4 points; Akua and Samek with a range from 1 to 5; Olorunleke et al. [ 53 ] used the grade; Petkeviciene et al. [ 57 ] with a range from 1 to 3 (from below to above average); de Souza et al. [ 54 ], Hernandez-Serrano et al. [ 35 ], and Paramo et al. [ 48 ] with a range from 0 to 10 points; Ong et al. [ 33 ] with a range from 0 to 7 points; and Mercado et al. [ 45 ] with a range from 1.4 to 3.5 points. Lukacs et al. [ 56 ] use an ordinal scale (poor, medium, good) like De la Cruz & Cebrino Cruz [ 49 ] (excellent, very good, good, discrete, bad, very bad). Arria et al. [ 42 ] evaluate the ability of the student to have or not a specific planning about academic duties. El Ansari et al. [ 34 ] evaluate the perception of the students about the importance of their performance, including performance rate; in El Ansari et al. [ 50 ] considered the importance to achieve a good grade, and comparative evaluation of their performance in relation to peers. Liguori and Lonbaken [ 43 ] evaluate the first–second year student retention, Tembo et al. [ 51 ] evaluate being late for class, missing classes, the inability to concentrate in class and inability to complete assignments with the Academic Role Expectation and Alcohol Scale (AREAS) [ 70 ] and finally Nasui et al. [ 55 ] evaluated skipping a class, missing class and receiving a lower grade after drinking. Risk of bias within studies Study designs were cross-sectional [ 33 , 48 , 51 , 52 , 54 – 57 ]. Petkeviciene, Kriaucioniene (57) used data from 3 surveys on 2000, 2010, and 2017. Longitudinal [ 15 , 41 , 42 , 44 , 46 , 47 ], descriptive [ 35 , 43 , 49 , 50 , 53 ], or retrospective [ 45 ]. The methodological quality of the studies increased from 2/16 to 10/16 points, and they can be considered from low to medium quality. The studies with higher quality reached 10/16 points [ 41 , 51 , 55 , 57 ]. These studies had clear aims, a random sample, a discrete sample [ 55 ], and a good sample size [ 51 ], and they clearly described [ 51 ] the inclusion criteria and subjective self-reported data [ 51 , 55 ]. The study with lower quality reached 2/16 points [ 53 ] because there was a convenience sample, no description of the characteristics of the sample, and no clear definition of outcome measurement. All studies had clear aims, but in general, the sample selection methodology was never probabilistic, except for Mekonen et al. [ 52 ]. Arria et al. [ 42 ], Hernandez-Serrano et al. [ 35 ], Liguori and Lonbaken [ 43 ], Meda et al. [ 44 ], Mekonen et al. [ 52 ], Mercado et al. [ 45 ], Nasui et al. [ 55 ], Piazza-Gardner et al. [ 47 ], de Souza et al. [ 54 ], and Tembo et al. [ 51 ] had clear inclusion criteria specified for the sample, but many of these studies use self-reported measurement (Additional file 3). 2.4 Summary statistics for meta-analysis Legal and illegal use of drugs and academic achievement We identified eleven studies [ 33 , 35 , 41 , 42 , 44 , 48 , 52 – 54 , 56 , 57 ] that assessed academic achievement in relation to substance consumption; however, only three studies [ 44 , 48 , 52 ] reported data for a meta-analysis. Considering these studies, we had 1,219 subjects in the control group and 350 drug consumers. The finding reveals a negative and significant effect of drug consumption on academic achievement. This effect can be considered of medium level (SMD = − 0.61; 95% CI -0.84 to − 0.38; p = 0.008). The heterogeneity of the studies was non-significant (I 2 = 0%, p = 0.489) (Fig. 2 ). Alcohol consumption and academic achievement All studies included in the systematic review reported data on alcohol consumption and academic achievement; however, four studies [ 15 , 44 , 48 , 52 ] were useful for assessing the meta-analysis. Considering these studies, we had 2,479 subjects in the control group and 7,134 alcohol consumers. The finding reveals that alcohol consumption had a small effect on academic achievement, as the pooled SMD (− 0.24) was not significant (95% CI − 0.51 to 0.04; p = 0.073). The heterogeneity between the studies was high (I2 = 82%, p < 0.001), but this heterogeneity was not qualitative because no study declared that students with alcohol consumption had better performance compared to students in the control group, except for the differences in the effect size estimated by each study (Fig. 3 ). Publication bias assessment Funnel plots (Fig. 4 and Fig. 5 ) seemed to be not present asymmetry but it was difficult to establish due to the few numbers of studies in both meta-analyses and the tests for funnel plot asymmetry could be not used since there were less than 10 studies. Discussion This systematic review provides quantitative evidence on the relationship between legal and illegal use of drugs among university students and academic achievement. Three studies [ 44 , 48 , 52 ] reported data for a meta-analysis that included 1,219 subjects in the control group and 350 drug consumers. The finding reveals a negative and significant effect of drug consumption on academic achievement. This effect can be considered at the medium level. Furthermore, four studies [ 15 , 44 , 48 , 52 ] that considered 2,479 subjects in the control group and 7,134 alcohol consumers reveal that alcohol consumption had a small effect on academic achievement. The studies useful for the meta-analysis are four only; however, collectively include a substantial number of students, which enhances the overall statistical power of the meta-analysis. A larger sample size allows for more reliable and generalizable conclusions. The heterogeneity among the studies is high for the subgroup (alcohol and academic achievement); however, this heterogeneity is not qualitative except for the differences in the sample dimension of every study. Previous studies reported mixed results [ 33 – 35 ], and this is the first meta-analysis that provides evidence on the effect of legal and illegal drug use on academic achievement among university students. The prevalence of substance use was high in the studies by Mekonen et al. [ 52 ], Meda et al. [ 44 ], and Paramo et al. [ 48 ], in which 28.6%, 57.2%, and 59.3%, respectively, of the students are substance abusers. Therefore, substance abuse in university students is a public health priority [ 3 , 22 ] due to negative consequences on health [ 1 , 3 ], decision making, attention and memory [ 12 , 71 ], and, in turn, academic achievement by increasing academic procrastination [ 17 ], as well as due to effects on the work market that cause financial loss [ 72 ]. Universities should take into account prevention and intervention programmes for substance abuse. Licciardone [ 73 ] found that these programmes are unlikely to be successful, but motivational interventions could be effective in reducing students’ drug use. Larimer et al. [ 74 ] found that many preventive and treatment programmes were effective in a variety of populations in decreasing substance abuse and that they could be adapted to university students. We believe that future research should focus on the effectiveness of preventive and treatment interventions to reduce substance abuse among university students. However, universities should anonymously monitor substance abuse among students over time to try to understand the extent of the phenomenon. Study limitations This study has some limitations. First, only a few studies were useful for the meta-analysis, and only two were longitudinal studies with a follow-up of two years [ 15 , 44 ]. The outcome was measured as GPA but with a different range score from 1 to 10 for Paramo et al. [ 48 ] and from 1 to 4 for An et al. [ 15 ] and Mekonen et al. [ 52 ], while Meda et al. [ 44 ] did not declare this outcome. Furthermore, the heterogeneity of the studies was not significant about substance abuse in general and academic achievement, but it was high in the studies that analysed the effect of alcohol on academic achievement, except for differences in the sample dimension. Conclusions This systematic review provides quantitative evidence on the relationship between legal and illegal use of drugs among university students and academic achievement. Specifically, we found a significant medium effect of substance abuse in general and a small effect for alcohol consumption on academic achievement. Our original hypothesis was confirmed. This is the first quantitative synthesis on substance abuse and academic achievement. These findings should be useful for universities and help us to present other hypotheses about the interventions that could prevent or reduce substance abuse among university students. Universities should be involved in increasing student awareness about the damage from substance abuse, monitoring the substance abuse of students, and promoting preventive and treatment intervention programmes. Future research should focus on the efficacy of these programmes in higher education. Declarations Author contributions G.B., F.I., F.S., R.M., I.S., A.V., M.M.: Designed the study and conceived the data, extracted data, performed the analysis, interpretation of data, drafted the manuscript and approved it. A.P., S.U., M.C., E.V., and R.A assisted in designing the study and data, interpretation, prepared figures, searched and screened the studies, and critically reviewed the manuscript. All authors read and approved final manuscript. Funding This study received no funding. Ethics, Consent to Participate, and Consent to Publish declarations Not applicable. Data availability Available from the corresponding author on reasonable request. Competing interests The authors declare no competing interests. Clinical trial number Not applicable. References Grant BF, Goldstein RB, Saha TD, Chou SP, Jung J, Zhang H, et al. Epidemiology of DSM-5 Alcohol Use Disorder: Results From the National Epidemiologic Survey on Alcohol and Related Conditions III. JAMA Psychiatry. 2015;72(8):757-66. Grant BF, Saha TD, Ruan WJ, Goldstein RB, Chou SP, Jung J, et al. Epidemiology of DSM-5 Drug Use Disorder: Results From the National Epidemiologic Survey on Alcohol and Related Conditions-III. 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The Alcohol, Smoking and Substance Involvement Screening Test (ASSIST): development, reliability and feasibility. Addiction. 2002;97(9):1183-94. Centre for Epidemiology and Evidence. NSW Population Health Survey 2014 - Questionnaire. NSW Government; 2014. Varela J, Braña T, Real E, Rial A. Validación empírica do AUDIT (Cuestionario de Identificación dos trastornos debidos ó consumo de alcohol) na poboación xeral galega. Santiago de Compostela: Xunta de Galicia, Consellería de Sanidade-Sergas; 2005. Cuenca-Royo AM, Sanchez-Niubo A, Forero CG, Torrens M, Suelves JM, Domingo-Salvany A. Psychometric properties of the CAST and SDS scales in young adult cannabis users. Addict Behav. 2012;37(6):709-15. Legleye S, Piontek D, Kraus L, Morand E, Falissard B. A validation of the Cannabis Abuse Screening Test (CAST) using a latent class analysis of the DSM-IV among adolescents. Int J Methods Psychiatr Res. 2013;22(1):16-26. McGee R, Kypri K. Alcohol-related problems experienced by university students in New Zealand. Aust N Z J Public Health. 2004;28(4):321-3. Hall W, Degenhardt L. Adverse health effects of non-medical cannabis use. Lancet. 2009;374(9698):1383-91. Rosario P, Costa M, Nunez JC, Gonzalez-Pienda J, Solano P, Valle A. Academic procrastination: associations with personal, school, and family variables. Span J Psychol. 2009;12(1):118-27. Licciardone JC. Outcomes of a federally funded program for alcohol and other drug prevention in higher education. Am J Drug Alcohol Abuse. 2003;29(4):803-27. Larimer ME, Kilmer JR, Lee CM. College Student Drug Prevention: A Review of Individually-Oriented Prevention Strategies. Journal of Drug Issues. 2005;35(2):431-56. Additional Declarations No competing interests reported. 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1","display":"","copyAsset":false,"role":"figure","size":237167,"visible":true,"origin":"","legend":"\u003cp\u003eFlowchart of preferred reporting items for systematic reviews and meta-analyses (PRISMA) study selection. Create using PRISMA Flow Diagram Tool [40]\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6221134/v1/4a1d7d1f733758914353a8f9.png"},{"id":80749931,"identity":"45431a55-cf7b-447d-9b94-b25d2c2acc19","added_by":"auto","created_at":"2025-04-16 16:09:01","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":73028,"visible":true,"origin":"","legend":"\u003cp\u003eForest plot of meta-analysis on the consumption of legal and illegal substances and academic achievement.\u003c/p\u003e\n\u003cp\u003eSD, standard deviation; \u003cem\u003eI\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e, heterogeneity of the studies; SMD, standardised mean difference\u003c/p\u003e","description":"","filename":"floatimage21.png","url":"https://assets-eu.researchsquare.com/files/rs-6221134/v1/d8a2b6373c61e63a48646e3c.png"},{"id":80749932,"identity":"d9f15b8b-728b-4774-b95a-c99110b23d95","added_by":"auto","created_at":"2025-04-16 16:09:01","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":86363,"visible":true,"origin":"","legend":"\u003cp\u003eFunnel plot for consumption of legal and illegal substances and academic achievement meta-analysis\u003c/p\u003e\n\u003cp\u003eSD, Standard Deviation; l2, heterogeneity of the studies; SMD, standardised mean difference.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6221134/v1/75cb9362c6c627a3b9a120ca.png"},{"id":80749135,"identity":"1c2931e6-57d7-42a2-8747-947c0fc51688","added_by":"auto","created_at":"2025-04-16 16:01:01","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":57951,"visible":true,"origin":"","legend":"\u003cp\u003eForest plot of the meta-analysis on alcohol consumption and academic achievement\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6221134/v1/6560f32537cdfbb0bd2d10ad.png"},{"id":80749933,"identity":"b1e66076-6a70-4efc-a5e0-a88349d6291c","added_by":"auto","created_at":"2025-04-16 16:09:01","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":58867,"visible":true,"origin":"","legend":"\u003cp\u003eFunnel plot for Alcohol consumption and academic achievement meta-analysis\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6221134/v1/980fb1c122db496048e44cfb.png"},{"id":86180577,"identity":"28ad9105-6d7d-483b-af8c-66de023e71b9","added_by":"auto","created_at":"2025-07-07 16:22:27","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1389399,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6221134/v1/0c5b17e3-a1ab-4870-9d4c-ae2928dedc4f.pdf"},{"id":80749133,"identity":"72eb2cb6-392d-40db-8219-554bdd00e823","added_by":"auto","created_at":"2025-04-16 16:01:01","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":14874,"visible":true,"origin":"","legend":"","description":"","filename":"Additionalfile1.docx","url":"https://assets-eu.researchsquare.com/files/rs-6221134/v1/195bdc9fbede4290779eddf7.docx"},{"id":80750411,"identity":"0cf5cd4b-9b28-4c62-a336-e402c6f65131","added_by":"auto","created_at":"2025-04-16 16:17:01","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":24160,"visible":true,"origin":"","legend":"","description":"","filename":"Additionalfile2.docx","url":"https://assets-eu.researchsquare.com/files/rs-6221134/v1/2969e8f1723bcf067226e091.docx"},{"id":80749138,"identity":"bd00bb8a-5419-4aba-a227-700be2b2e213","added_by":"auto","created_at":"2025-04-16 16:01:01","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":30221,"visible":true,"origin":"","legend":"","description":"","filename":"Additionalfile3.docx","url":"https://assets-eu.researchsquare.com/files/rs-6221134/v1/cd5bdecbffbcb209824f5da0.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Substance abuse and academic performance among university students: systematic review and meta-analysis","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSubstance abuse is a widespread concern among young adults [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e–\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] and is particularly significant among college students. University students represent a high-risk group for both legal and illegal drug use, as this academic period often marks their first experience with reduced parental oversight [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] and introduces stressors related to new relationships and the challenges of successful adaptation [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Substance abuse in this population is linked to numerous academic, physical, mental, and social difficulties. Research indicates that nearly half of college students meet the criteria for at least one substance use disorder (SUD), and young adults aged 19–30 report elevated rates of cannabis use, vaping (both cannabis and nicotine), and hallucinogen use [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. This issue presents serious public health implications, contributing to increased rates of morbidity and mortality [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e–\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Specifically, alcohol abuse is associated with mental disorders [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], highly disabling outcomes [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], and physical and psychiatric comorbidities [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Some studies have shown that excessive alcohol consumption and substance use are associated with difficulties in adapting to academic life, poor working memory and reasoning [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], lower intelligence, and reduced attention in both adolescents and college students [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. In addition, other consequences are decreased academic performance [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], less time studying, disengagement from academic duties [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], and increased academic procrastination [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. High levels of academic failure are a great problem for universities' reputation because they can lose potential new students [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Contrasting academic failure means also promoting human development and increasing the social and cultural capital of the country, creating the conditions for economic development and the progress of society [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. In addition, students generally do not use only one drug but more substances together [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], and these associations can further aggravate the negative consequences of academic failure of university students.\u003c/p\u003e\n\u003ch3\u003eConsumption of legal and illegal drugs among university students\u003c/h3\u003e\n\u003cp\u003eIn Western countries, the consumption of legal and illegal drugs has increased in recent years among the university population [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. In the United States, among college students and young people, the frequency of binge drinking (consuming four/five or more drinks for women/men) and substance use is high (30–40%) [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. In Finland, 22% of college students smoke, 21% use illicit drugs, 41% are high-frequency drinkers, and 31.4%, 16.3%, and 6.7% show one, two, or three abuse-associated behaviours (alcohol, tobacco, and other drugs), respectively [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Consumption of tobacco, alcohol, and illegal drugs like cannabis is prevalent among Spanish university students [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], and alcohol use is common in 18–24-year-old people who reported the habit of drinking, binge drinking [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFadhel [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] assessed substance abuse among university students in Yemen and Saudi Arabia and found that 12.5% of students use sedative drugs, and the overall prevalence of drug abuse was low (27.2%), moderate (10.5%), substantial (2.1%) and severe (0.8%). In Egypt, Kabbash et al., [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] found that university students use cigarettes (8.9%), tranquilisers (4.3%), hashish (3.6%), alcohol (2.7%), bhang (1.4%), and tramadol (1.0%). In Africa, among Tunisian university students, the prevalence of high-risk alcohol consumption and alcoholic disorder is 52.5% and 79.1%, respectively [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e], and in Ethiopia, the prevalence of alcohol consumption is 35.5% [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eNumerous studies have investigated the association between academic achievement and the use of legal or illegal substances among university students. While some research indicates that substance abuse and alcohol consumption negatively impact academic performance [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e], other studies have found no significant relationship between these variables [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThis study aims to systematically review quantitative literature exploring the relationship between legal and illegal drug use among university students and academic achievement. Specifically, it seeks to determine whether drug consumption behavior has an effect on academic performance.\u003c/p\u003e "},{"header":"Methods","content":"\u003cp\u003eA systematic literature review and meta-analysis was conducted. The PRISMA guidelines guided the processes of source selection, data extraction, and data presentation [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThis review protocol was registered in the Open Science Framework.\u003c/p\u003e\n\u003ch3\u003eEligibility criteria\u003c/h3\u003e\n\u003cp\u003eWe formulate a research question based on the PICO method: Population (university student), Intervention (legal or illegal drug use), Comparison (no substance abuse), and Outcome (academic achievement). For the topic, we decided on the following inclusion criteria: any empirical quantitative study design regarding university students\u0026rsquo; substance abuse (alcohol, tobacco, cannabis, and other legal and illegal drugs) and academic achievement in peer-reviewed journals in every language. Exclusion criteria are empirical studies regarding substance abuse and academic achievement in non-university students, articles without full text available, conferences, editorials, theses and books, case reports, case series, and systematic review studies. No data frame was considered.\u003c/p\u003e\n\u003ch3\u003eInformation sources\u003c/h3\u003e\n\u003cp\u003eThe literature search was developed based on medical subject headings (MeSH), keywords, and free-text words related to university students, alcohol abuse, and academic achievement. We performed the search in electronic databases, including MEDLINE, CINHAL, Scopus, and ERIC. In addition, in PROSPERO, updated in January 2025. We researched ongoing or recently completed systematic reviews.\u003c/p\u003e\n\u003ch3\u003eSearch strategy\u003c/h3\u003e\n\u003cp\u003eThe mesh terms, keywords, and free-text words used in the search strategy were combined with the Boolean operator \u0026ldquo;AND\u0026rdquo;/\u0026ldquo;OR\u003cem\u003e\u0026rdquo;\u003c/em\u003e (\u0026ldquo;Students\u0026rdquo;, OR \u0026ldquo;School enrolment\u0026rdquo;, OR \u0026ldquo;Universities\u0026rdquo;) AND (Alcohol-Induced Disorders\u0026rdquo;, OR \u0026ldquo;Alcohol drinking\u0026rdquo;, OR \u0026ldquo;Binge Drinking\u0026rdquo;, OR \u0026ldquo;Abuse, Marijuana\u0026rdquo;, OR \u0026ldquo;Hashish Abuse\u0026rdquo;, OR \u0026ldquo;Cannabis Abuse\u0026rdquo;, OR \u0026ldquo;Substance-Related Disorders\u0026rdquo;, OR \u0026ldquo;Cannabis Related Disorders\u0026rdquo;, OR \u0026ldquo;Drug Use Disorders\u0026rdquo;, OR \u0026ldquo;Substance Abuse\u0026rdquo;, OR \u0026ldquo;Substance Addiction\u0026rdquo;, OR \u0026ldquo;Drug Dependence\u0026rdquo;) AND (Academic success\u0026rdquo;, OR \u0026ldquo;Academic achievement\u0026rdquo;, OR Academic performance\u0026rdquo;, OR \u0026ldquo;Academic test score\u0026rdquo;) (Additional file 1).\u003c/p\u003e\n\u003ch3\u003eSelection process\u003c/h3\u003e\n\u003cp\u003eThree researchers (I. S., R. M., G. B.) independently examined the studies based on the title and abstract. All records obtained from the literature search were collected into the Endnote library to delete duplicates. In this phase, the researchers decided the studies to include based on eligibility criteria (empirical studies, concerning university students, evaluating substance abuse and academic achievement, written in all languages). We scanned the references of all included studies. The studies were excluded for lack of precision of the research question, a different population from that of interest (adolescent, primary and secondary students), and academic success not measured quantitatively. Academic achievement was defined as the performance obtained in the programme by the student as the grade point average in every situation (course, cumulative GPA at the end of the year and from one year to another). Substance abuse was defined as all substances (legal or illegal drug) assumed by the university student. When there was a doubt about including a study, the study was included for discussion in the final decision with the agreement of everyone. In case of disagreement among researchers, a senior researcher\u0026rsquo;s intervention was considered. When some study was excluded, the reasons were declared. We also performed a manual search analysing the references from the included studies. Each step performed independently was discussed for agreement in the large group of researchers.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eData collection process\u003c/h2\u003e \u003cp\u003eAll data extracted were collected in an Excel sheet. Three researchers (I. S., R. M., G. B.) extracted data independently, and, in case of disagreement, reviewers resolved it by discussion. We contacted the study authors to resolve any doubt.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eData items\u003c/h3\u003e\n\u003cp\u003eWe collected the following data from each study: author name, year of publication, country, aim of the study, study design, overall sample size, demographic characteristics, instrument used to measure the substance use, instrument to measure the academic achievement, the number of students with substance abuse (any definition: only alcohol use, alcohol\u0026thinsp;+\u0026thinsp;any drug use, binge drinking, etc.), the number of students without substance abuse. In case of a longitudinal study, we collected the time at which the analysis was performed. When a study consisted of multiple groups, such as a different group based on drug consumption frequency, we combined the groups to have only one group of student drug consumers. We collected data on the quantitative modality of the assessment of academic achievement and we considered the average, standard deviation, standard error (SE), median, range, and interquartile range of academic success in students not consuming drugs and those consuming drugs. If effect sizes cannot be calculated, we contacted the authors for additional data.\u003c/p\u003e\n\u003ch3\u003eOutcomes and prioritisation\u003c/h3\u003e\n\u003cp\u003eThe primary outcome was the effect of substance abuse on academic achievement.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eRisk of bias assessment\u003c/h2\u003e \u003cp\u003eThe risk of bias was assessed using the Edward score [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e] for observational studies. The 11 items of the assessment tool are as follows: definition of aims, sample formation, description of inclusion and exclusion criteria, description of subject characteristics, power calculation, objectivity of outcome measures used, adequacy of follow-up, adequacy of analysis (intention to treat), adjustment for baseline differences between groups, appropriate unit of allocation to groups, and randomisation method. Each item is scored from 0 to 2 for adequacy, and a high score indicates a study\u0026rsquo;s high methodological quality. The total score possible ranges from 0 to 22 for experimental studies and from 0 to 16 for observational studies.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eEffect measures\u003c/h2\u003e \u003cp\u003eThe standardized mean difference (SMD) was chosen as summary statistic to synthesize the effect of drug consumption behaviour on academic achievement.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eData synthesis\u003c/h2\u003e \u003cp\u003eIf the studies are sufficiently homogeneous in terms of drug consumption definition and sample population, we conducted meta-analyses using a random-effects model. Meta-analysis was the statistical technique used to synthesise results when mean and standard deviation (SD) of academic achievement in drug/alcohol consumers group and in non-consumers group were available. A random-effects mode was performed, with DerSimonian and Laird estimation of the between-study variance.\u003c/p\u003e \u003cp\u003eA forest plot was used to represent the meta-analysis results. The heterogeneity between the studies was assessed by visual inspection of the forest plot and by the overlap of the CIs and possible outliers, and it was quantified through the I\u003csup\u003e2\u003c/sup\u003e index. The I\u0026sup2; statistic describes the percentage of variation across studies that is due to heterogeneity rather than chance. We considered that an I\u003csup\u003e2\u003c/sup\u003e of 25% indicated low heterogeneity, 50% moderate, and 75% high [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. A p value of the chi-squared (χ2) test, a statistical test for heterogeneity, was included in the forest plot.\u003c/p\u003e \u003cp\u003eA possible source of heterogeneity (e.g., mean age) was not investigated by meta-regression since there are fewer than 10 studies [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. Publication bias was assessed with visual inspection of the funnel plot, that is, a scatter plot of the effect estimates from individual studies against SE. The funnel plot asymmetry was not verified due to the small number of studies included in the meta-analysis.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eStudy selection\u003c/h2\u003e \u003cp\u003eWe combined the three search strings (1#2#3), retrieving a total of 1,477 records. After removing 48 duplicates, 1,429 unique records remained. The last search was conducted in January 2025. After screening titles and abstracts, 1,370 records were excluded as they were not relevant to our research aims. The remaining 59 studies underwent full-text evaluation. Of these, 38 studies were excluded for the following reasons: they did not focus on academic achievement (n\u0026thinsp;=\u0026thinsp;11), were not empirical studies (n\u0026thinsp;=\u0026thinsp;8), did not consider university students (n\u0026thinsp;=\u0026thinsp;8), did not quantify academic success (n\u0026thinsp;=\u0026thinsp;4), or were reviews (n\u0026thinsp;=\u0026thinsp;7). As a result, 21 studies were included in the final selection (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), of which four were deemed suitable for meta-analysis.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eStudy characteristics\u003c/h2\u003e \u003cp\u003eWe included 21 studies (Additional file 2). The time frame for publication is from 2007 to 2023. The countries more represented were the USA with eight studies [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan additionalcitationids=\"CR42 CR43 CR44 CR45 CR46\" citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e], Spain with three studies [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e], the United Kingdom with two studies [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e], and one study each in Qatar [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e], Ethiopia [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e], Nigeria [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e], Brasil [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e], Romania [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e], Hungary [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e], Lithuania [\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e] and Australia [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. The studies considered different types of university students coming from different courses, public or private universities, and different sample sizes, with a minimum of 129 students [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e] and a maximum of 23,518 [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe consumption of legal or illegal drugs was measured with different instruments, and different substances were considered with single or aggregate data. An et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], El Ansari et al. [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e], El Ansari et al. [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e], Liguori and Lonbaken [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e], Mercado et al. [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e], Nasui et al. [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e], Pascarella et al. [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e], Piazza-Gardner et al. [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e], and Tembo et al. [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e] evaluated only alcohol consumption. An et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], El Ansari et al. [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e], Liguori and Lonbaken [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e], Pascarella et al. [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e], and Piazza-Gardner et al. [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e] classify the level of abuse behaviours with one or more items. El Ansari et al. [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] use the CAGE [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e]; Mercado et al. [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e] use the Short Alcohol Dependence Data Questionnaire (SADD) Raistrick et al. [\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e]; [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e] use AUDIT [\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e]; Tembo et al. [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e] use the AUDIT [\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e]; and Nasui et al. [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e] use the Romanian version of the Student Alcohol Questionnaire [\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e]. Ache Akua and Samek [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e] evaluate alcohol and cannabis consumption with two items. Olorunleke et al. [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e] considered alcohol and tabacco and evaluated them with a structured questionnaire. Petkeviciene et al. [\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e] considered alcohol, drug use (ecstasy, cocaine, LSD, cannabis,\u0026hellip;) and smoking and evaluated them with a questionnaire for drung and smoking, while used the CAGE questionnaire for alcohol abuse and dependence [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e]. Arria et al. [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e], Hernandez-Serrano et al. [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e], Lukacs et al. [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e], Meda et al. [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e], Mekonen et al. [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e], Ong et al. [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e], Paramo et al. [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e], and de Souza et al. [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e] assess more than one drug use. Arria et al. [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e] evaluates alcohol and marijuana, inhalants, heroin, cocaine, hallucinogens, amphetamine/methamphetamine, and ecstasy consumption. For alcohol dependence, Arria et al. [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e] use the DSM-IV criteria based on the questionnaire from the Substance Abuse and Mental Health Services Administration [\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e], while they use some questions for the other substances. de Souza et al. [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e] assess alcohol, marijuana, and cocaine use with the Alcohol, Smoking, and Substance Involvement Screening Test (ASSIST) [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e]. Hernandez-Serrano et al. [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e] assess alcohol, cannabis and tobacco use; Lukacs et al. [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e] assess alcohol, tobacco, ecstasy, depressant, and herbal drug use; Meda et al. [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] assesses alcohol and marijuana use; and Mekonen et al. [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e] assess alcohol, smoking, and other substances with the ASSIST [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e]. Ong et al. [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e] assess alcohol and smoking use with the NSW questionnaire [\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e], and Paramo et al. [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e] assess alcohol use with the AUDIT-C [\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e, \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e] and cannabis use with the CAST [\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e, \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAcademic achievement was assessed with self-reported data [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan additionalcitationids=\"CR34\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan additionalcitationids=\"CR46\" citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e, \u003cspan additionalcitationids=\"CR50 CR51 CR52 CR53 CR54 CR55 CR56\" citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e] or by administrative database [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. Meda et al. [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] and Paramo et al. [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e] use the GPA, while Liguori and Lonbaken [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e] use the first\u0026ndash;second year retention.\u003c/p\u003e \u003cp\u003eFor self-reported data, An et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], Mekonen et al. [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e], and Piazza-Gardner et al. [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e] used the GPA with a range from 1 to 4 points; Akua and Samek with a range from 1 to 5; Olorunleke et al. [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e] used the grade; Petkeviciene et al. [\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e] with a range from 1 to 3 (from below to above average); de Souza et al. [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e], Hernandez-Serrano et al. [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e], and Paramo et al. [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e] with a range from 0 to 10 points; Ong et al. [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e] with a range from 0 to 7 points; and Mercado et al. [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e] with a range from 1.4 to 3.5 points. Lukacs et al. [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e] use an ordinal scale (poor, medium, good) like De la Cruz \u0026amp; Cebrino Cruz [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e] (excellent, very good, good, discrete, bad, very bad). Arria et al. [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e] evaluate the ability of the student to have or not a specific planning about academic duties. El Ansari et al. [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] evaluate the perception of the students about the importance of their performance, including performance rate; in El Ansari et al. [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e] considered the importance to achieve a good grade, and comparative evaluation of their performance in relation to peers. Liguori and Lonbaken [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e] evaluate the first\u0026ndash;second year student retention, Tembo et al. [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e] evaluate being late for class, missing classes, the inability to concentrate in class and inability to complete assignments with the Academic Role Expectation and Alcohol Scale (AREAS) [\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e] and finally Nasui et al. [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e] evaluated skipping a class, missing class and receiving a lower grade after drinking.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eRisk of bias within studies\u003c/h2\u003e \u003cp\u003eStudy designs were cross-sectional [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e, \u003cspan additionalcitationids=\"CR55 CR56\" citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e]. Petkeviciene, Kriaucioniene (57) used data from 3 surveys on 2000, 2010, and 2017. Longitudinal [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e], descriptive [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e, \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e], or retrospective [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe methodological quality of the studies increased from 2/16 to 10/16 points, and they can be considered from low to medium quality. The studies with higher quality reached 10/16 points [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e, \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e, \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e]. These studies had clear aims, a random sample, a discrete sample [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e], and a good sample size [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e], and they clearly described [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e] the inclusion criteria and subjective self-reported data [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e, \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e]. The study with lower quality reached 2/16 points [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e] because there was a convenience sample, no description of the characteristics of the sample, and no clear definition of outcome measurement. All studies had clear aims, but in general, the sample selection methodology was never probabilistic, except for Mekonen et al. [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. Arria et al. [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e], Hernandez-Serrano et al. [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e], Liguori and Lonbaken [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e], Meda et al. [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e], Mekonen et al. [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e], Mercado et al. [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e], Nasui et al. [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e], Piazza-Gardner et al. [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e], de Souza et al. [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e], and Tembo et al. [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e] had clear inclusion criteria specified for the sample, but many of these studies use self-reported measurement (Additional file 3).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Summary statistics for meta-analysis\u003c/h2\u003e \u003cdiv id=\"Sec19\" class=\"Section3\"\u003e \u003ch2\u003eLegal and illegal use of drugs and academic achievement\u003c/h2\u003e \u003cp\u003eWe identified eleven studies [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan additionalcitationids=\"CR53\" citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e, \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e] that assessed academic achievement in relation to substance consumption; however, only three studies [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e] reported data for a meta-analysis. Considering these studies, we had 1,219 subjects in the control group and 350 drug consumers. The finding reveals a negative and significant effect of drug consumption on academic achievement. This effect can be considered of medium level (SMD\u0026thinsp;=\u0026thinsp;\u0026minus;\u0026thinsp;0.61; 95% CI -0.84 to \u0026minus;\u0026thinsp;0.38; p\u0026thinsp;=\u0026thinsp;0.008). The heterogeneity of the studies was non-significant (I\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0%, p\u0026thinsp;=\u0026thinsp;0.489) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e\u003c/p\u003e\n\u003ch2\u003eAlcohol consumption and academic achievement\u003c/h2\u003e\n\u003cp\u003eAll studies included in the systematic review reported data on alcohol consumption and academic achievement; however, four studies [\u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e52\u003c/span\u003e] were useful for assessing the meta-analysis. Considering these studies, we had 2,479 subjects in the control group and 7,134 alcohol consumers. The finding reveals that alcohol consumption had a small effect on academic achievement, as the pooled SMD (\u0026minus;\u0026thinsp;0.24) was not significant (95% CI \u0026minus;\u0026thinsp;0.51 to 0.04; p\u0026thinsp;=\u0026thinsp;0.073). The heterogeneity between the studies was high (I2\u0026thinsp;=\u0026thinsp;82%, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), but this heterogeneity was not qualitative because no study declared that students with alcohol consumption had better performance compared to students in the control group, except for the differences in the effect size estimated by each study (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cdiv id=\"Sec21\" class=\"Section2\"\u003e\n \u003ch2\u003ePublication bias assessment\u003c/h2\u003e\n \u003cp\u003eFunnel plots (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e \u003cstrong\u003eand\u003c/strong\u003e Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e) seemed to be not present asymmetry but it was difficult to establish due to the few numbers of studies in both meta-analyses and the tests for funnel plot asymmetry could be not used since there were less than 10 studies.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis systematic review provides quantitative evidence on the relationship between legal and illegal use of drugs among university students and academic achievement. Three studies [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e] reported data for a meta-analysis that included 1,219 subjects in the control group and 350 drug consumers. The finding reveals a negative and significant effect of drug consumption on academic achievement. This effect can be considered at the medium level. Furthermore, four studies [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e] that considered 2,479 subjects in the control group and 7,134 alcohol consumers reveal that alcohol consumption had a small effect on academic achievement. The studies useful for the meta-analysis are four only; however, collectively include a substantial number of students, which enhances the overall statistical power of the meta-analysis. A larger sample size allows for more reliable and generalizable conclusions. The heterogeneity among the studies is high for the subgroup (alcohol and academic achievement); however, this heterogeneity is not qualitative except for the differences in the sample dimension of every study. Previous studies reported mixed results [\u003cspan additionalcitationids=\"CR34\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e], and this is the first meta-analysis that provides evidence on the effect of legal and illegal drug use on academic achievement among university students.\u003c/p\u003e \u003cp\u003eThe prevalence of substance use was high in the studies by Mekonen et al. [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e], Meda et al. [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e], and Paramo et al. [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e], in which 28.6%, 57.2%, and 59.3%, respectively, of the students are substance abusers. Therefore, substance abuse in university students is a public health priority [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] due to negative consequences on health [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], decision making, attention and memory [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e], and, in turn, academic achievement by increasing academic procrastination [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], as well as due to effects on the work market that cause financial loss [\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eUniversities should take into account prevention and intervention programmes for substance abuse. Licciardone [\u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e73\u003c/span\u003e] found that these programmes are unlikely to be successful, but motivational interventions could be effective in reducing students\u0026rsquo; drug use. Larimer et al. [\u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e] found that many preventive and treatment programmes were effective in a variety of populations in decreasing substance abuse and that they could be adapted to university students. We believe that future research should focus on the effectiveness of preventive and treatment interventions to reduce substance abuse among university students. However, universities should anonymously monitor substance abuse among students over time to try to understand the extent of the phenomenon.\u003c/p\u003e \u003cdiv id=\"Sec23\" class=\"Section2\"\u003e \u003ch2\u003eStudy limitations\u003c/h2\u003e \u003cp\u003eThis study has some limitations. First, only a few studies were useful for the meta-analysis, and only two were longitudinal studies with a follow-up of two years [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. The outcome was measured as GPA but with a different range score from 1 to 10 for Paramo et al. [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e] and from 1 to 4 for An et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] and Mekonen et al. [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e], while Meda et al. [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] did not declare this outcome. Furthermore, the heterogeneity of the studies was not significant about substance abuse in general and academic achievement, but it was high in the studies that analysed the effect of alcohol on academic achievement, except for differences in the sample dimension.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThis systematic review provides quantitative evidence on the relationship between legal and illegal use of drugs among university students and academic achievement. Specifically, we found a significant medium effect of substance abuse in general and a small effect for alcohol consumption on academic achievement. Our original hypothesis was confirmed. This is the first quantitative synthesis on substance abuse and academic achievement. These findings should be useful for universities and help us to present other hypotheses about the interventions that could prevent or reduce substance abuse among university students. Universities should be involved in increasing student awareness about the damage from substance abuse, monitoring the substance abuse of students, and promoting preventive and treatment intervention programmes. Future research should focus on the efficacy of these programmes in higher education.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eG.B., F.I., F.S., R.M., I.S., A.V., M.M.: Designed the study and conceived the data, extracted data, performed the analysis, interpretation of data, drafted the manuscript and approved it. A.P., S.U., M.C., E.V., and R.A assisted in designing the study and data, interpretation, prepared figures, searched and screened the studies, and critically reviewed the manuscript. All authors read and approved final manuscript.\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study received no funding.\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eEthics, Consent to Participate, and Consent to Publish declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAvailable from the corresponding author on reasonable request.\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eClinical trial number\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eGrant BF, Goldstein RB, Saha TD, Chou SP, Jung J, Zhang H, et al. 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Journal of Drug Issues. 2005;35(2):431-56.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-medical-education","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"meed","sideBox":"Learn more about [BMC Medical Education](http://bmcmededuc.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/meed/default.aspx","title":"BMC Medical Education","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"alcohol drinking, drug use disorders, university student, academic achievement","lastPublishedDoi":"10.21203/rs.3.rs-6221134/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6221134/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground.\u003c/h2\u003e \u003cp\u003eSubstance abuse is a widespread concern among young adults and is particularly significant among college students. Substance abuse in this population is linked to numerous academic, physical, mental, and social difficulties. This systematic review and metanalysis explores whether there is an effect of the illegal drug and alcohol consumption behaviors on academic achievement among university students.\u003c/p\u003e\u003ch2\u003eMethods.\u003c/h2\u003e \u003cp\u003eThe databases searched were MEDLINE, CINHAL, Scopus, ERIC, and PROSPERO, updated in January 2025. The risk of bias was assessed using the Edward score. We used a random-effects model. The protocol of this review was registered in the Open Science Framework.\u003c/p\u003e\u003ch2\u003eResults.\u003c/h2\u003e \u003cp\u003eThe systematic review included 21 studies, while the meta-analysis included four studies. In a sample of 1,219 subjects in the control group and 350 illegal drug consumers, there is a negative and significant effect of drug consumption on academic achievement [SMD\u0026thinsp;=\u0026thinsp;\u0026minus;\u0026thinsp;0.61 (95% CI \u0026minus;\u0026thinsp;0.84 to \u0026minus;\u0026thinsp;0.38; p\u0026thinsp;=\u0026thinsp;0.008). In a subgroup analysis, a sample of 2,479 subjects in the control group and 7,134 alcohol consumers, there is a small effect of alcohol consumption on academic achievement [SMD\u0026thinsp;=\u0026thinsp;\u0026minus;\u0026thinsp;0.24 (95% CI -0.51 to 0.04; p\u0026thinsp;=\u0026thinsp;0.073).\u003c/p\u003e\u003ch2\u003eConclusions.\u003c/h2\u003e \u003cp\u003eThis systematic review provides quantitative evidence on the relationship between legal and illegal use of drugs among university students and academic achievement. Specifically, we found a significant medium effect of substance abuse in general and a small effect for alcohol consumption on academic achievement.\u003c/p\u003e","manuscriptTitle":"Substance abuse and academic performance among university students: systematic review and meta-analysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-16 16:00:56","doi":"10.21203/rs.3.rs-6221134/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-05-12T04:31:47+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-28T09:32:43+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-25T16:37:54+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-07T18:22:15+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"122959889235517083971833663922512178379","date":"2025-04-07T15:18:45+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"180875574326046086603813600194111739904","date":"2025-04-07T14:46:08+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"216288385017640571564963905410785298729","date":"2025-04-04T11:02:36+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-03-28T09:30:11+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-03-27T07:23:05+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-03-26T10:27:58+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-03-26T10:27:14+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Medical Education","date":"2025-03-13T14:42:23+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-medical-education","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"meed","sideBox":"Learn more about [BMC Medical Education](http://bmcmededuc.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/meed/default.aspx","title":"BMC Medical Education","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"89b3121e-0288-4ab2-8164-16ab4b1798da","owner":[],"postedDate":"April 16th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-07-07T16:17:57+00:00","versionOfRecord":{"articleIdentity":"rs-6221134","link":"https://doi.org/10.1186/s12909-025-07530-y","journal":{"identity":"bmc-medical-education","isVorOnly":false,"title":"BMC Medical Education"},"publishedOn":"2025-07-01 15:57:24","publishedOnDateReadable":"July 1st, 2025"},"versionCreatedAt":"2025-04-16 16:00:56","video":"","vorDoi":"10.1186/s12909-025-07530-y","vorDoiUrl":"https://doi.org/10.1186/s12909-025-07530-y","workflowStages":[]},"version":"v1","identity":"rs-6221134","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6221134","identity":"rs-6221134","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}