With growing public interest in mental health, applications connected to smartwatches have be-come increasingly common, offering users tools to monitor and manage their well-being. This thesis examines how message framing affects users’ willingness to share personal and sensitive data in the context of digital mental health services. It further explores differences in sharing behaviour between first-party and third-party recipients, as well as the influence of users’ self-reported mental health status. A web-based between-subjects experiment was conducted, in which participants were exposed to one of three transparency framing conditions (altruistic, egoistic, or neutral). Willingness to share data was measured alongside trust, privacy concerns, and personality traits. Results showed that participants were significantly more willing to share data with first-party recipients than with third parties. Individuals with a mental health condition reported higher overall willingness to share sensitive data. However, message framing had no significant effect on sharing behaviour. This study contributes to the practical understanding of willingness to share in mental health applications, offering insights for designers, policymakers, and stakeholders to develop privacy conscious and trust strategies that align with users’ expectations and concerns.