Objectives: Analyse reported processes of co-design and co-production in the context of health and social care to explore the underlying mechanisms that enable inclusive and reciprocal engagement.

Search strategy: Peer review research was obtained from a prior scoping review searching eight databases consisting of all methodologies relevant to co-design or co-production in the context of health and social care services and involving service-users.

Methods of selection: Articles were included for synthesis if they reported a process of dialogue, with mutuality, insight and clarification in their engagement process. Ninety-three peer-review articles informed our programme theory development.

Analysis: Data relating to co-design and co-production processes were extracted and analysed through inductive, abductive, and deductive analysis leading to the development of an initial programme theory.

Main results: This realist synthesis finds that co-design and co-production can occur at different times, in part or all of the research and participatory process. There is an over reliance on the term ‘co-design’ or ‘co-production’ to convey complex engagement or participatory processes. We identified six mechanisms (intention, assets, dialogue, documentation, interpretation and understanding). Interaction between these six identified mechanisms in context, even if only brief, is important for supporting meaningful engagement, alignment and agreement within a co-design or co-production process.

Implications for practice: The initial programme theory presented in this article provides clarity by identifying essential mechanisms which can guide the design and implementation of a range of participatory approaches. Rather than relying on a single label to convey complex participatory methods or processes, the values and principles of co-design or co-production, in combination with this programme theory, could be applied to guide implementation and reporting of specific activities within a range of research or participatory methods.

Patient and public contribution: The initial programme theory was presented and piloted in a series of collaborative workshops between May 2023 and March 2024 with patient and public contributors, health professionals and researchers. This engagement process is currently underway to refine the programme theory and it is anticipated that this next phase will be completed in September 2024.

The aim of this review was to understand what needs to happen for meaningful engagement to take place by exploring how co-design and co-production in health and social care has been reported in published research. Ninety-three research articles were selected as these reported engagement processes with exchanges of mutual insight. Articles which only stated that engagement took place, without reporting details, were excluded. Any information relating to co-design and co-production processes were then extracted and analysed. The findings from this review were that co-design and co-production can occur at different times, in part or all of the research and engagement process. We identified that interaction between six key elements (intention, assets, dialogue, documentation, interpretation and understanding) in context, even if only brief, are important for meaningful engagement to occur within a co-design or co-production process. We also found that there is an over reliance on the term ‘co-design’ or ‘co-production’ to convey complex processes for engagement. Rather than relying on a single word to convey such complex methods or processes, the values and principles of co-design or co-production, in combination with the key elements identified, could be applied to guide implementation, and reporting of specific activities within a range of research methods.