Background <p>Digital health interventions, particularly those delivered via mobile health, are transforming the way health prevention is provided. Evaluating user participation and its contribution to intervention outcomes is key to ensuring the effectiveness of an intervention. This study aims to identify conditions shaping user participation in MedPrev, a digital health intervention designed to deliver prevention in primary care.</p> Methods <p>We conducted a theory-driven qualitative study following the Consolidated Criteria for Reporting Qualitative Research (COREQ). A conceptual framework for user participation was developed prior to data collection, informed by a scoping review and co-creation workshops with stakeholders, which did not constitute data for the present study. Data collection then combined interviews with patients (<i>n</i> = 8) and health professionals (<i>n</i> = 5) with observations of MedPrev consultations (<i>n</i> = 10) across two French regions. Thematic analysis was performed using NVivo® software. Our findings were subsequently validated and refined through three deliberative workshops involving users, health professionals, and program designers (<i>n</i> = 19 participants).</p> Results <p>Participation in MedPrev intervention is influenced by interdependent factors relating to professional and organizational settings, digital interventions, and user conditions. Three key themes emerged from the analysis: i) professional/organizational context, characterized by factors such as physician shortages, time constraints, and physician training in prevention; ii) intervention design elements, including technical barriers (e.g., web-based platform, login complexity) and lack of personalization; and iii) user factors, encompassing digital literacy, health literacy, and life circumstances.</p> Conclusion <p>User participation in digital health interventions is closely related to contextual factors. A systemic approach is essential in any attempt to address barriers related to adoption and usage, and to optimize the effectiveness of user participation in MedPrev and similar interventions. Recommendations include facilitating adoption, improving the feasibility of human intervention, personalizing the digital intervention, and strengthening hybrid follow-up approaches to combine digital and human interaction. Specific recommendations emphasize the value of hybrid models that combine digital innovations with human support to make digital preventive interventions effective and to ensure long-term engagement.</p>