A systematic review of the effectiveness of peer-based interventions on health-related behaviors in adults.

We reviewed 25 randomized clinical trials that assessed the effect of peer-based interventions on health-related behaviors in adults. Effect sizes were calculated as odds ratios or standardized mean differences. We grouped most of the studies by 7 measured outcomes, with effect sizes ranging from -0.50 to 2.86. We found that peer-based interventions facilitated important changes in health-related behaviors, including physical activity, smoking, and condom use, with a small- to medium-sized effect. However, the evidence was mixed, possibly because of the heterogeneity we found in methods, dose, and other variables between the studies. Interventions aimed at increasing breastfeeding, medication adherence, women's health screening, and participation in general activities did not produce significant changes.