Patient and public involvement is widely thought to be important in the improvement of health care delivery and in health equity. Purpose: The article examines the role of experiential knowledge in service co-production in order to develop opiate substitution treatment services (OST) for high-risk opioid users. Method: Drawing on social representations theory and the concept of social identity, we explore how experts’ by experience and registered nurses’ understandings of OST contain discourses about the social representations, identity, and citizenship of the (...) participants and the effects these may have on developing or hindering inclusive and bottom-up forms of patient and public involvement. Results: The meeting sessions that potentially offer room for creativity and problem-solving fail to provide any new propositions for fixing the system. The health care professionals primarily identify themselves as regulators who protect the correctness of their actions and show little interest in considering experiential knowledge on opioid addiction. Conclusion: The participation of patients has been one of the prominent reforms implemented in health care. The goal of client-centered thinking is often emphasised; however, the implementation is not simple due to the strongly institutionalised knowledge and related working patterns and practices in health care. (shrink)