Abstract: We included 11 randomised controlled trials involving 2796 people. The quality of these studies was moderate to low, with most of the studies at unclear risk of bias in terms of random sequence generation and allocation concealment, and high risk of bias for blinded outcome assessment and selective outcome reporting. Five trials involving 581 people compared consumer-providers to professionals in similar roles within mental health services (case management roles (4 trials), facilitating group therapy (1 trial)). There were no significant differences in client quality of life (mean difference (MD) -0.30, 95% confidence interval (CI) -0.80 to 0.20); depression (data not pooled), general mental health symptoms (standardised mean difference (SMD) -0.24, 95% CI -0.52 to 0.05); client satisfaction with treatment (SMD -0.22, 95% CI -0.69 to 0.25), client or professional ratings of client-manager relationship; use of mental health services, hospital admissions and length of stay; or attrition (risk ratio 0.80, 95% CI 0.58 to 1.09) between mental health teams involving consumer-providers or professional staff in similar roles. There was a small reduction in crisis and emergency service use for clients receiving care involving consumer-providers (SMD -0.34 (95%CI -0.60 to -0.07). Past or present consumers who provided mental health services did so differently than professionals; they spent more time face-to-face with clients, and less time in the office, on the telephone, with clients' friends and family, or at provider agencies. Six trials involving 2215 people compared mental health services with or without the addition of consumer-providers. There were no significant differences in psychosocial outcomes (quality of life, empowerment, function, social relations), client satisfaction with service provision (SMD 0.76, 95% CI -0.59 to 2.10) and with staff (SMD 0.18, 95% CI -0.43 to 0.79), attendance rates (SMD 0.52 (95% CI -0.07 to 1.11), hospital admissions and length of stay, or attrition (risk ratio 1.29, 95% CI 0.72 to 2.31) between groups with consumer-providers as an adjunct to professional-led care and those receiving usual care from health professionals alone. One study found a small difference favouring the intervention group for both client and staff ratings of clients' needs having been met, although detection bias may have affected the latter. None of the six studies in this comparison reported client mental health outcomes. No studies in either comparison group reported data on adverse outcomes for clients, or the financial costs of service provision. Involving consumer-providers in mental health teams results in psychosocial, mental health symptom and service use outcomes for clients that were no better or worse than those achieved by professionals employed in similar roles, particularly for case management services. There is low quality evidence that involving consumer-providers in mental health teams results in a small reduction in clients' use of crisis or emergency services. The nature of the consumer-providers' involvement differs compared to professionals, as do the resources required to support their involvement. The overall quality of the evidence is moderate to low. There is no evidence of harm associated with involving consumer-providers in mental health teams. Future randomised controlled trials of consumer-providers in mental health services should minimise bias through the use of adequate randomisation and concealment of allocation, blinding of outcome assessment where possible, the comprehensive reporting of outcome data, and the avoidance of contamination between treatment groups. Researchers should adhere to SPIRIT and CONSORT reporting standards for clinical trials. Future trials should further evaluate standardised measures of clients' mental health, adverse outcomes for clients, the potential benefits and harms to the consumer-providers themselves (including need to return to treatment), and the financial costs of the intervention. They should utilise consistent, validated measurement tools and include a clear description of the consumer-provider role (eg specific tasks, responsibilities and expected deliverables of the role) and relevant training for the role so that it can be readily implemented. The weight of evidence being strongly based in the United States, future research should be located in diverse settings including in low- and middle-income countries.

Plain-language summary: We conducted a systematic review, comprehensively searching databases and other materials to identify randomised controlled trials which involved past or present consumers of mental health services employed as providers of mental healthcare services for adult clients. To be included, studies had to make one of two comparisons: 1) consumer-providers versus professionals employed to do the same role within a mental health service, or 2) mental health services with and without consumer-providers as an adjunct to the service. We found 11 randomised controlled trials involving approximately 2796 people. The quality of the evidence is moderate to low; it was unclear in many cases whether steps were taken to minimise bias, both in the way that participants were allocated to groups, and in how the outcomes were assessed and reported. Five of the 11 trials involving 581 people compared consumer-providers to professionals who occupied similar roles within mental health services (case management roles (4 trials), and facilitating group therapy (1 trial)). There were no significant differences between the two groups, in terms of client (care recipient) quality of life, mental health symptoms, satisfaction, use of mental health services, or on the numbers of people withdrawing from the study. People receiving care from past or present users of mental health services used crisis and emergency services slightly less than those receiving care from professional staff. Past or present consumers who provided mental health services did so differently than professionals; they spent more time face-to-face with clients, and less time in the office, on the telephone, with clients' friends and family, or at provider agencies. Six of the 11 trials, involving 2215 people, compared mental health services with or without the addition of consumer-providers. There were no significant differences in quality of life, empowerment, function and social relations, in client satisfaction, attendance rates, hospital use, or in the numbers of people withdrawing from the study, between groups with consumer-providers as an adjunct to professional care and those receiving usual care by health professionals alone. None of these six studies reported on clients' mental health symptoms. None of the studies reported on adverse outcomes (harms) for clients, or on the costs of providing the services. Overall, we concluded that employing past or present consumers of mental health services as providers of mental health services achieves psychosocial, mental health symptom and service use outcomes that are no better or worse than those achieved by professional staff in providing care. There is no evidence that the involvement of consumer-providers is harmful. More high-quality and well-reported randomised trials are needed, particularly to evaluate mental health outcomes, adverse outcomes for clients, the potential benefits and harms to the consumer-providers themselves (including a need to return to treatment), and whether it is cost-effective to employ them. Future researchers should include a clear description of the consumer-provider role and relevant training for the role so that it can be readily implemented, and should investigate consumer-providers in settings outside the United States.