Peer Review Report For: Barriers and enablers to implementing capacity-strengthening initiatives for public and patient involvement in mental health research: a scoping review protocol informed by the Consolidated Framework for Implementation Research [version 1; peer review: 1 approved, 2 approved with reservations]

Background Public and Patient Involvement (PPI) in mental health research is increasingly recognised as a moral and ethical imperative, necessary to increase the relevance and effectiveness of translation of research findings. Despite policy mandates and growing evidence of its benefits, PPI implementation in mental health research remains inconsistent. Little attention has been given to the state of scientific knowledge on PPI capacity strengthening in mental health research that can support more meaningful implementation. The aims of this scoping review are to: determine the state of knowledge concerning PPI in mental health research capacity-strengthening initiatives; identify the outcome measures used to evaluate the impact of capacity strengthening initiatives for PPI on contributors, research processes, and policy; and map the barriers and enablers to the implementation of capacity strengthening initiatives for PPI. Methods This scoping review will follow JBI and PRISMA-ScR guidelines. Sources will include peer-reviewed articles, grey literature, and organisational materials describing training or skill-building initiatives for adult PPI contributors in mental health research. Searches will be conducted in MEDLINE, Embase, PsycINFO, and CINAHL, supplemented by hand-searching, targeted internet searches, and stakeholder consultation. Data extraction will capture descriptive details, initiative content, outcomes, and contextual factors, with barriers and enablers categorised according to the Consolidated Framework for Implementation Research (CFIR) domains. Conclusion This review will provide the first comprehensive synthesis of capacity-strengthening initiatives for PPI contributors in mental health research. Findings will inform the development of a co-designed blueprint for capacity-strengthening for PPI contributors, and progress broader efforts to embed lived experience expertise and general public perspectives equitably within mental health research systems.