User involvement has received increasing attention in health research in recent years to strengthen the relevance, legitimacy, and societal value of research. At the same time, existing studies indicate that the implementation and practice of user involvement are often associated with challenges, particularly related to mechanisms of power between user representatives and professionals, which may shape collaboration. A better understanding of how mechanisms of power manifest in user involvement processes is therefore essential for advancing user involvement in health research. This study explores which mechanisms of power can be identified in user involvement processes in Danish health research. The study adopts a qualitative case study design, examining user involvement within a Danish research project. The empirical material consists of seven semi-structured interviews with user representatives and professionals affiliated with the project, as well as one observation of a meeting among the project’s professionals. The analysis was conducted as a thematic analysis, structured through Roura’s framework, and interpreted through Foucault’s understanding of power. The findings show that mechanisms of power emerge through different understandings of user involvement and its value among actors, through the ways in which collaboration between professionals and user representatives is structured, and through organizational and institutional frameworks for research projects. The study contributes to an understanding of how mechanisms of power may shape collaboration in user involvement processes and highlights implications for the practice of user involvement in health research.