Objective:
Peer support has been shown to support personal recovery from mental illness. It is unclear whether the effects of peer support across different mental illnesses depend on the organizational setting. The authors reviewed the effectiveness of peer support for both personal recovery and clinical recovery of adults with any mental illness and evaluated the effectiveness of peer support in different settings.

Methods:
A systematic review of randomized controlled trials (RCTs) was conducted in PubMed, PsycInfo, CINAHL, Cochrane Library, and Web of Science. A meta-analysis of outcomes of personal and clinical recoveries at the end of interventions was conducted.

Results:
In total, 49 RCTs with 12,477 participants with any mental illness were included. Most of the trials had a high risk for bias. Results of the meta-analysis indicated that peer support in general had a small positive effect on personal recovery (standard mean difference [SMD]=0.20; 95% CI=0.11–0.29) and decreased anxiety symptoms (SMD=−0.21; 95% CI=−0.40 to −0.02), with most trials evaluating peers added to mental health–related hospital services. No data for peers in established service roles were available for the meta-analysis. Peer-designed interventions developed to be provided independently of hospital services and delivered in community settings had a modest effect on self-advocacy. A small nonsignificant effect on personal recovery for peer support delivered online was also observed.

Conclusions:
The effect on personal recovery from mental illness was most evident in peer support added to hospital services. High-quality RCTs with comparable cocreated interventions and clear descriptions of mechanisms of change are needed to further investigate peer support efficacy.