This paper considers proposals for developing ‘co-productive’ medical partnerships, within the UK National Health Service (NHS), concentrating in particular on the potential problem involved in combining professional and lay conceptions of health. Much of the literature that advocates the introduction of co-productive healthcare partnerships assumes that medical professionals and patients share, or can easily come to share, a common set of beliefs about what is valuable with regard to health interventions and outcomes. However, a substantial literature documents the contestability of (...) the concept of health, particular across professional and lay divides. We suggest that this potential disagreement ought to be taken seriously, and suggest that the prospect of a co-productive NHS in which patients and professionals act in partnership is threatened by the existence of unresolved epistemic differences. We suggest that part of the solution may lie in re-framing this potential disagreement in the terms provided by Engel’s bio-psycho-social account of health, and demonstrate how support for this account can be grounded upon a critical realist foundation. What we call a ‘stratified conception of health’ reveals the potential complementarity between health beliefs which may have at first seemed to be essentially contradictory. We consider some of the practical implications this idea has for conceiving and creating co-productive medical partnerships. (shrink)