Medical evidence had been built through research led by experts, and patients, who participated mainly as study subjects. Gradually, patients' subjectivity (e. g., the effect of drugs, quality of life) has been adopted in research results. In recent years, "Patient and Public Involvement (PPI)" evolved, and more patients have been involved in research planning, research implementation, and utilization of results. Hence, the patient's empirical knowledge is gradually added to the evidence built up by specialized knowledge, thus changing the entire body of medical knowledge. PPI takes a different form depending on the research design and how patients are involved. Service user-led research and co-production are expected to be suitable for drawing up empirical knowledge, and the results of those studies in the UK and other countries inform medical policies and clinical guidelines. This article will examine the effects of service user-led research and co-production on psychiatry and introduce co-production research conducted by the author with patients who have undergone compulsory hospitalization. We hope this article will serve as a hint for implementing PPI and co-production in Japanese psychiatry in the future.
 Author's abstract