Background <p>Incorporating lived experiences into research is claimed to enhance depth, relevance, real-world applicability and equity. However, data scientists have been relatively slow to adopt this approach. The “Depression Detectives” (DD) project aimed to bridge this gap by connecting Big Data researchers with individuals with lived experience of depression. Depression is both a significant global health issue and a deeply personal experience. Feelings of isolation often drive people to seek information and support online, making this project’s digital presence particularly relevant.</p> Methods <p>Building on methods developed in Parenting Science Gang, we conducted a co-production project within a private Facebook group from February to September 2021. Seventy individuals with depression and thirty researchers participated in discussions and chose a research question. Together, they designed and implemented a survey and focus groups exploring health-seeking behaviours and under-reporting of depressive episodes to GPs. Concurrently, a PhD student analysed UK Biobank data for discrepancies in depression reporting. We used multiple methods to evaluate the process and participant experiences.</p> Co-produced research results <p>In the UK Biobank, 67% of individuals whose questionnaire responses indicated depression had no coded GP record of it. Similarly, 84% of DD participants reported visiting their GP for half or fewer of their depressive episodes. Key barriers included stigma, dissatisfaction with healthcare, and a preference for non-medical interventions. These alternatives were perceived as better addressing the root causes of depression.</p> Evaluation results <p>Participants described the research process as rewarding, noting it broadened their understanding both of depression and their own experiences. Researchers valued the insights gained, but found the process demanding.</p> Conclusions <p>This project demonstrates the value of incorporating lived experiences into mental health research through co-production. Lived experience participants contributed unique perspectives that differed from those of university researchers. By combining these insights with big data analysis, the project generated findings that better reflect real-life experiences, enhancing their applicability to personalised mental health care. Participants found the process to be ‘quasi-therapeutic’ and advocated for healthcare systems to adopt diverse, holistic treatments for depression. These findings support inclusive policy development and underscore the importance of epistemic justice and democratic knowledge production.</p>