Abstract
Background Adults with mental illness who also experience social marginalization face interconnected clinical and social challenges, yet scalable interventions addressing both dimensions of recovery remain limited.Aims To evaluate the effects of group-based community interventions on social reintegration and mental health among socially marginalized adults with mental illness.Methods We conducted a preregistered systematic review and meta-analysis of interventions delivered in OECD countries. Searches identified 28,980 records; 62 studies met the inclusion criteria and 49 studies, contributing 349 effect sizes, were included in the meta-analysis. Outcomes were classified as social reintegration or mental health. Meta-analytic models accounted for dependent effect sizes within studies.Results Group-based community interventions improved social reintegration (g = 0.195, 95% CI [0.122, 0.268]) and mental health (g = 0.215, 95% CI [0.090, 0.340]) relative to control conditions, corresponding to effects approximately 2.3 and 1.4 times larger, respectively, than the typical improvements under treatment as usual. Effects varied substantially across studies and outcomes, while measured moderators explained little of this heterogeneity. Effects on social reintegration and mental health were positively associated. Findings were robust across sensitivity analyses and showed little indication of publication bias. Nearly half of studies were preregistered and contributed approximately two-thirds of all effect sizes. Preregistered studies yielded smaller social reintegration effects than non-preregistered studies, although the average effect remained statistically significant and substantively meaningful.Conclusions Group-based community interventions can improve both social reintegration and mental health among marginalized adults with mental illness, suggesting that they may support multidimensional recovery. Their potential value therefore extends beyond scalability and lower delivery costs to substantively meaningful improvements in outcomes. However, substantial unexplained heterogeneity indicates that benefits are unlikely to be uniform across populations, interventions, and settings.What is already known on this topicAdults experiencing both mental illness and social marginalization face interconnected clinical and social challenges, while existing systematic reviews on group-based interventions have largely focused on specific diagnoses, intervention types, or psychiatric symptoms.What this study addsAcross 49 studies contributing 349 effect sizes, group-based community interventions produced positive average effects on both social reintegration and mental health. Effects in the two domains were positively associated, but substantial heterogeneity remained largely unexplained.