Background Patient and public involvement in research is required by many applied health research funding bodies. However, co-production, where patient/public contributors are involved in partnership at every stage of study design/conduct, is unusual; particularly with potentially ‘vulnerable’ and marginalised groups. Little evidence reports the practicalities or outcomes of such work. The aim of this study is to evaluate involvement of peer researchers (PRs) with lived experience of co-occurring alcohol and mental health problems in old age to co-produce qualitative research, and co-design new initiatives in health services to support this patient population.

Methods Eight PRs with lived experience co-produced qualitative research (interviews, workshops) to inform intervention development. PRs informed project conception/design, co-facilitated interviews/workshops, and contributed to data interpretation and dissemination. Their involvement/contributions were evaluated via an impact log and realist evaluation.

Results PRs identified a gap in patient care that meant they were left unsupported by existing care systems. They contributed to effective recruitment materials and pathways via their insights and networks, ensuring recruitment was successful. PRs supported collection of rich qualitative data by promoting participants’ openness through rapport developed by shared experiences; and probing interviewees in view of their own experiences to deepen understanding. During data analysis, PRs identified intricacies and themes within data that were not recognised by the academic research team. PRs identified unmet support needs from interview data; and potential initiatives to address these through their own experiences with recovery and related services. PRs contributed to impactful dissemination activities, augmenting study findings through their own experiences; particularly targeting practitioners and policymakers to inform changes in commissioning and practice. PRs’ personal networks, skill-sets, external roles (e.g. as peer support workers within alcohol/mental health services) and insights supported these activities. Proactive management of PRs’ mental health, digital exclusion and confidence issues were important; and required clear buddying/distress protocols, good working relationships, empathy, encouragement, training and resources (financial/technological) to ensure inclusion and effective involvement. PRs benefited from involvement; emphasising how their role contributed to recovery from their alcohol/mental health problems, and positive self-identity following their experiences of these stigmatising conditions; building confidence and a perception that they were actively contributing to society; as well as financial reimbursement to contribute to household finances.

Discussion PRs’ involvement ensured the study addressed a gap in care for this marginalised patient group; successful conduct and rich data and analysis. Supporting PRs’ work in view of their support needs was central to effective involvement.