Substance Use Prevalence and Patterns in Vulnerable Populations: A Systematic Review and Meta-Analysis

OBJECTIVE: The purpose of this study was to estimate the prevalence and patterns of alcohol and other drug use among vulnerable populations and to assess the quality and certainty of the evidence using PRISMA 2020 (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) reporting standards and GRADE (Grading of Recommendations Assessment, Development and Evaluation) criteria. METHOD: A systematic review and meta-analysis were conducted according to the PRISMA 2020 guidelines. Searches in PubMed, Scopus, Web of Science, PsycINFO, and Embase (2010-2025) identified observational studies reporting substance use among vulnerable groups (refugees, migrants, homeless individuals, and socially excluded adolescents). Eighteen studies comprising more than 98,000 participants (approximately two thirds male) were included. Data were extracted independently, and pooled prevalence estimates were calculated using random-effects models (DerSimonian-Laird estimator) in JASP Version 0.19.3. Risk of bias was assessed with the Joanna Briggs Institute tools, and evidence certainty was rated using the GRADE framework. RESULTS: = 95%). Higher prevalence was observed among homeless and displaced adults compared with adolescents and migrants. The overall certainty of evidence was rated as moderate. CONCLUSIONS: Substance use--particularly non-alcohol drugs--is markedly more prevalent among vulnerable populations than in the general population. Social exclusion, homelessness, and forced migration amplify risk and highlight the need for integrated prevention, harm-reduction, and mental-health strategies tailored to these groups. These findings can inform policy design and targeted interventions in humanitarian and low-resource contexts.