"You can kind of just feel the power behind what someone's saying": a participatory-realist evaluation of peer support for young people coping with complex mental health and substance use challenges.

<bold>Background: </bold>Youth peer support, as a practice that aligns youth engagement and participatory approaches, has become increasingly popular in the context of youth mental health services. However, there is a need for more evidence that describes how and why youth peer support practice might be effective. This study was designed to examine a peer support service for youth experiencing complex challenges with mental health, physical health and/or substance use to better understand key features and underlying mechanisms that lead to improved client outcomes.<bold>Methods: </bold>We applied a hybrid realist-participatory approach to explore key issues and underlying theoretical assumptions within a youth peer support approach for young people (age 14-26) experiencing complex mental health and substance use challenges. We used semi-structured interviews and focus groups with staff, including peers (N = 8), clinical service providers and administrative staff (N = 15), to develop the theories and a client survey to validate them. Our qualitative thematic analysis applied a retroductive approach that involved both inductive and deductive processes. For the client survey (N = 77), we calculated descriptive statistics to examine participant profiles and usage patterns. Pearson correlations were examined to determine relationships among concepts outlined in the program theories, including context, mechanism and outcome variables.<bold>Results: </bold>Our analyses resulted in one over-arching context, one over-arching outcome and four program theories. Program theories were focused on mechanisms related to 1) positive identity development through identification with peers, 2) enhanced social connections, 3) observational learning and 4) enhanced autonomy and empowerment.<bold>Conclusions: </bold>This study serves as a unique example of a participatory-realist hybrid approach. Findings highlight possible key components of youth peer practice and shed light on the functional mechanisms that underlie successful peer practice. These key components can be examined in other settings to develop more comprehensive theories of change with respect to youth peer support and can eventually be used to develop guidelines and standards to strengthen practice. This research contributes to an expanding body of literature on youth peer support in mental health and connects peer practice with several social theories. This research begins to lay a foundation for enhanced youth peer support program design and improved outcomes for young people experiencing complex mental health and substance use challenges. [ABSTRACT FROM AUTHOR]