AbstractBackgroundThe benefits of peer support interventions (PSIs) for individuals with mental illness are not well known. The aim of this systematic review and meta-analysis was to assess the effectiveness of PSIs for individuals with mental illness for clinical, personal, and functional recovery outcomes.MethodsSearches were conducted in PubMed, Embase, and PsycINFO (December 18, 2020). Included were randomized controlled trials (RCTs) comparing peer-delivered PSIs to control conditions. The quality of records was assessed using the Cochrane Collaboration Risk of Bias tool. Data were pooled for each outcome, using random-effects models.ResultsAfter screening 3455 records, 30 RCTs were included in the systematic review and 28 were meta-analyzed (4152 individuals). Compared to control conditions, peer support was associated with small but significant post-test effect sizes for clinical recovery, g = 0.19, 95% CI (0.11–0.27), I² = 10%, 95% CI (0–44), and personal recovery, g = 0.15, 95% CI (0.04–0.27), I² = 43%, 95% CI (1–67), but not for functional recovery, g = 0.08, 95% CI (−0.02 to 0.18), I² = 36%, 95% CI (0–61). Our findings should be considered with caution due to the modest quality of the included studies.ConclusionsPSIs may be effective for the clinical and personal recovery of mental illness. Effects are modest, though consistent, suggesting potential efficacy for PSI across a wide range of mental disorders and intervention types.