Agoal of primary care research is to inform and facilitate beneficial change in health care delivery for both patients and clinicians in a way that is efficient for providers and economically sustainable for the health care system. Co-design or co-creation is a process whereby researchers and stakeholders jointly contribute to the ideation, planning, implementation and evaluation of new services and systems as a possible means to optimise the impact of research findings.1,2 Co-creation represents the highest form of stakeholder engagement, building on existing theories such as community-based participatory research,3 and emphasises the creation of value for both end users and researchers. However, it is often infeasible to co-create with all stakeholders at all stages of a research project. Decisions must be made about which stakeholders to involve at different stages to achieve the greatest return on investment for researchers’ and stakeholders’ time and contributions, considering the context in which change is likely to occur. In designing a controlled pilot study of a multifaceted intervention to reduce inappropriate polypharmacy in primary care involving 20 general practitioners and more than 150 patients in south-east Queensland, we identified both patients and prescribers as the most important stakeholders. For this project, however, we proposed that the critical gateway to effective co-creation in the first instance was the GP, with both the GP and patient to be involved in evaluating the pilot to inform future development. In this article, we describe the rationale for this approach, the process, challenge and value of cocreating with GPs in the planning and implementation of the intervention, and the anticipated value of involving both patients and GPs in the pilot’s evaluation.