Introduction Peer online mental health forums are commonly used and offer accessible support. Positive and negative impacts have been reported by forum members and moderators, but it is unclear why these impacts occur, for whom and in which forums. This multiple method realist study explores underlying mechanisms to understand how forums work for different people. The findings will inform codesign of best practice guidance and policy tools to enhance the uptake and effectiveness of peer online mental health forums. Methods and analysis In workstream 1, we will conduct a realist synthesis, based on existing literature and interviews with approximately 20 stakeholders, to generate initial programme theories about the impacts of forums on members and moderators and mechanisms driving these. Initial theories that are relevant for forum design and implementation will be prioritised for testing in workstream 2. Workstream 2 is a multiple case study design with mixed methods with several online mental health forums differing in contextual features. Quantitative surveys of forum members, qualitative interviews and Corpus-based Discourse Analysis and Natural Language Processing of forum posts will be used to test and refine programme theories. Final programme theories will be developed through novel triangulation of the data. Workstream 3 will run alongside workstreams 1 and 2. Key stakeholders from participating forums, including members and moderators, will be recruited to a Codesign group. They will inform the study design and materials, refine and prioritise theories, and codesign best policy and practice guidance. Ethics and dissemination Ethical approval was granted by Solihull Research Ethics Committee (IRAS 314029). Findings will be reported in accordance with RAMESES (Realist And MEta-narrative Evidence Syntheses: Evolving Standards) guidelines, published as open access and shared widely, along with codesigned tools. Trial registration number ISRCTN 62469166; the protocol for the realist synthesis in workstream one is prospectively registered at PROSPERO CRD42022352528.
Background: Online forums are used widely to facilitate mental health peer support. However, concerns exist regarding potential harm associated with their use, and little is known about forum safety from the user perspective. Objective: This study sought to understand how users experience safety within online mental health peer support forums. Following previous research, safety was conceptualized with reference to both experiences of harm and feelings of interpersonal safety within the forum environment. Methods: Data was collected from 42 semi-structured realist interviews and 504 cross-sectional survey responses from users of three UK-based online mental health forums. These included a forum hosted by a health service provider with sub-forums for anxiety, depression, and eating disorders; a corporate provider focused on young people’s mental health; and a voluntary sector provider with sub-forums for general mental health support, eating disorders, and postpartum psychosis. A bespoke survey was used to obtain descriptive quantitative data regarding user perceptions of forum safety. Qualitative data was used to refine an initial programme theories framework comprising context-mechanism-outcome configurations related to forum safety developed in previously published realist synthesis. Results: Survey responses revealed that over half of participants felt safe to post because of online anonymity (40.1% agreed, 19.2% strongly agreed), while a minority reported encountering distressing forum posts (18.8% agreed, 3.6% strongly agreed) and expressed concern that talking about mental health online could make them feel worse (22.4% agreed, 3.4% strongly agreed). Refined programme theories highlight: (1) the disclosure-promoting effect of anonymity, related to the mitigation of concerns that users’ mental health experiences could be linked to their offline identities; (2) the importance of proactive content moderation for addressing emerging safety issues; (3) a need for organizations to implement rule enforcement sensitively and balance between conversational openness and restricting topics likely to cause distress; (4) forum users’ experiences of self-moderating their exposure to potentially distressing online content; and (5) how the perceived non-judgement, authenticity, and similarity of other forum users generates interpersonal safety. Conclusions: This is the first realist evaluation to directly assess processes underpinning safety in online mental health forums. A key novel finding of this study is that safety emerges not only from harm reduction procedures but also a facilitative interpersonal atmosphere defined by sensitive moderation and the sharing of lived experiences. Hosts should therefore remain attentive to both potential risks and opportunities to foster connections between community members.