Programme Theory 1 refinement process.

Intersectoral Collaboration (ISC) involves multiple sectors working together to tackle complex challenges that no single sector can address alone. In global health, where interconnected issues demand holistic approaches, ISC aligns goals and resources to enhance effectiveness and equity. However, power dynamics within and between sectors can either foster synergy or create tensions, shaping ISC outcomes. This study explores how, why, for whom, in what contexts, and to what extent power dynamics influence ISC in a northeastern state of India. A realist evaluation was conducted in Assam, India. Six Programme Theories (PTs) from a prior realist review were tested and refined through theory-driven realist interviews with 18 stakeholders across different sectors. Data were analysed using Context-Mechanism-Outcome Configurations (CMOCs) to refine PTs, offering a nuanced understanding of how individual, institutional, and contextual factors influence ISC outcomes. A total of 62 CMOCs, grouped into 17 demi-regularities, refined six PTs on power dynamics in ISC. Fair participation fostered empowerment, while proactive leadership enhances motivation, though resource gaps may weaken these effects. Fair resource allocation reduced power imbalances, improving collaboration, whereas hierarchy and unclear roles breed distrust. Personal relationships helped build trust and overcome hierarchy. Findings emphasise that improving ISC requires attention to both structural and relational mechanisms through designing programs that leverage both of these. Given this single-district, qualitative case study, the findings are context-specific to Dibrugarh, Assam, and should be transferred cautiously to comparable settings. Future research could refine programme theories into a middle-range theory, enhancing their transferability to other settings.