The pooled results from randomized controlled trials indicate that peer support interventions improve depression symptoms more than usual care alone and that the effects may be comparable to those of group cognitive behavioral therapy. The estimated effect size of peer support vs. usual care for symptoms of depression (0.59) is similar to those recently reported in meta-analyses of psychotherapy trials for depression (0.67, or 0.42 after correcting for publication bias) and of published antidepressant medication trials (0.41) [45
]. These findings suggest that peer support interventions have the potential to be effective components of depression care, and they provide evidence in support of expert opinion advocating for peer support to be included in recovery-oriented mental health treatment[7
We found significant heterogeneity across studies comparing peer support to usual care and we were able to account for this heterogeneity by stratifying based on whether depression was assessed under conditions blinded to treatment assignment. The pooled effect size was much smaller for blinded studies than for unblinded studies (−0.21 vs. −0.95, respectively), suggesting internal bias amongst the unblinded studies. Based on this more conservative estimate of effect size, peer support may be less efficacious than some established evidence-based treatments for depression (i.e. antidepressant medications). Interestingly, a recent meta-analysis of psychotherapy for depression found the effect size to also be much lower among high quality studies (0.22 for high-quality studies vs. 0.68 for all studies) and comparable to the effect size for peer support when blinded assessments were used[47
]. The observed positive effect of peer support, coupled with its potential low cost and scalability, may therefore make it an attractive alternative when other depression care interventions (including those with modestly larger effects) are unavailable, unaffordable, or unacceptable.
Our generally positive results should be viewed in the context of a mixed literature on peer support for general medical conditions and health behaviors, alcohol dependence (i.e. Alcoholics Anonymous), and serious mental illness[18
]. Collectively, meta-analyses and reviews in these other areas indicate that peer support may be an effective intervention for patients with a variety of health concerns; however, much of the evidence is limited by the use of observational data or by the heterogeneous methods used to deliver and assess peer support in controlled trials.
The results of our meta-analysis are also limited in that many of the included studies drew from several distinct subpopulations of depressed individuals (i.e., post-partum women, men with HIV). While this may improve the generalizability of our findings to depressed patients with co-morbid general medical conditions, our findings may actually be less generalizable to depressed patients that have no other co-occuring condition in common. The paucity of available studies also limited our ability to conduct stratified analyses or meta-regression analyses to explore potentially important determinants of depression outcomes associated with peer support interventions, such as comorbidity, initial depression severity, or length of intervention. Our study is also limited in that the fidelity of the group cognitive behavioral therapy and the treatment that “usual care” participants received were not available to be included in the meta-analysis. It is also possible that our search strategy, which included only peer-reviewed publications, may have missed some eligible and influential studies. Our analyses, however, did not show evidence of publication bias or that any one study influenced the results. Ongoing and future studies of peer support may influence the results in subsequent meta-analyses.
Future research should employ larger randomized controlled trials, particularly among a more broadly representative population of patients with depression in primary care settings, in order to better characterize those patients for whom peer support would be most efficacious. In addition, the optimal approach to providing peer support needs clarification. Although most existing trials’ interventions used in-person peer groups, the largest trial used a telephone-based intervention with pairs. Identifying whether one or the other method, or a combination of the methods, is more effective for certain patients is an important goal for future research. Other important research questions include whether there are differences in response between patients experiencing acute versus chronic depression, the optimal duration and frequency of peer interactions, the amount and type of prior training peers should receive, and whether there are specific patient characteristics that could be used in matching patients to peers in order to improve outcomes. While peer support has the potential to be delivered at low cost, the actual costs of delivering peer support (including training of peers and coordination of services) should be formally evaluated. Finally, future trials should seek to characterize the mechanisms by which peer support may provide therapeutic benefit.