AUSTRALIAN ADOLESCENT SOCIAL MEDIA USE AND MENTAL HEALTH BEFORE AND AFTER THE SOCIAL MEDIA MINIUM AGE LEGISLATION: A STUDY PROTOCOL

Introduction: Over the last two decades, increases in adolescent mental health difficulties have been recorded alongside a rapid expansion in social media use. In response to these trends, on December 10, 2025, the Australian government implemented Social Media Minimum Age legislation prohibiting Australians under the age of 16 years from having social media accounts. The introduction of this legislation allows for a unique quasi-experimental investigation of the impact of social media use on adolescent mental health, and the mechanisms through which social media may impact young Australian adolescents’ mental health, wellbeing and cognition.Methods and analysis: To assess the relationship between social media use and young adolescents’ mental health, wellbeing and cognition, a mixed-methods approach will be taken. 422 young people (aged 10-15 years) and parent/carer dyads were recruited and completed baseline assessment before the implementation of the Social Media Minimum Age legislation (October-December, 2025). Three follow-up assessments will be completed after 6-, 12- and 18-months. Data from longitudinal parent and adolescent surveys, ecological momentary assessments (EMA), cognitive tasks and smartphone recorded screenshots of social media and messaging app use will be analysed using linear regression and dynamic structural equation modelling. Ethics and dissemination: This study has been approved by the UNSW Human Research Ethics Committee (iRECS 9197). Findings from this study will help identify potential opportunities for interventions at an individual, micro (parental) and macro (governmental) level, to mitigate any negative impacts of social media for younger adolescents. Results will be disseminated through peer-reviewed publications, conference presentations, public engagement opportunities and researcher associated websites.Strengths and Limitations of this study: This study has been designed with several strengths, including:-ecological momentary assessments to capture mood, mental health symptoms and online exposures in close-to-real time, minimising recall bias; -a longitudinal design to capture changes within participants over time as well as inclusion of adolescents across a five-year age range, enabling comparison of developmental differences; -matched parent and child pairs to assess associations with digital parenting; -data collection conducted before and at three timepoints up to 12 months after the introduction of the Social Media Minimum Age legislation, enabling examination of the potential impacts of the Australian Government policy. A potential limitation is the reliance on participant retention across the study period to maintain sufficient statistical power for all analyses. To support retention, participants will receive updates on the research findings to highlight their contribution, as well as remuneration that increases incrementally across each stage of the study.