Optimizing Engagement with Digital Mental Health Resources Among Sexual and Gender Minority Users: Protocol for a Series of Microrandomized Trials

Background: Sexual and gender minority (SGM) populations experience significant mental health disparities, yet continue to face persistent barriers to care. Mental Health America (MHA) provides free, web-based screening and self-guided resources to millions of visitors, including tens of thousands of SGM visitors each year. Digital mental health (DMH) can facilitate access to mental health resources; however, engagement remains a central challenge that limits effectiveness. MHA faces similar engagement challenges, with preliminary analyses indicating that most visitors exit the website without accessing substantive mental health content pages. The QT-Digital Mental Health Engagement study uses an iterative approach to develop and test strategies for improving engagement with DMH resources among SGM users. Objective: This study provides the rationale and protocol for an iterative series of microrandomized trials testing theory-based engagement strategies embedded within the web infrastructure of a real-world DMH platform. The primary aim is to evaluate whether delivering engagement strategies increases SGM visitors' naturalistic engagement with MHA resources. Methods: Eligible participants will be MHA visitors who complete the Patient Health Questionnaire-9 depression screening test in English and indicate on an optional postscreening survey that they live in the United States, are aged ≥14 years, and identify as LGBTQ+ (lesbian, gay, bisexual, transgender, queer, and other SGM populations). Participants will be randomized at 2 decision points embedded within the MHA Online Screening Program. At each decision point, participants will be randomized with equal probability (0.2) to receive no engagement strategy or an engagement strategy targeting 1 of 4 Health Action Process Approach behavioral determinants, including outcome expectancy, risk perception, self-efficacy, or SGM-specific barriers to engagement. The primary outcome will be proximal engagement with MHA content, operationalized at decision point 1 as click-through to a targeted Next Steps Content Page and at decision point 2 as click-through to any additional MHA content page. The primary analysis will estimate the marginal causal excursion effect of delivering any engagement strategy compared with the control. Results: This study received funding from the National Institute of Mental Health in June 2023 (K01MH131795). The protocol was approved by the single institutional review board at the University of Washington on December 3, 2025 (STUDY00017726). Data collection began on March 12, 2026, and is projected to end in July 2026. As of April 13, 2026, a total of 3878 participants have been enrolled, with 52% (n=2004) of participants identifying as SGM visitors aged 14 to 17 years. Conclusions: This protocol describes an iterative series of microrandomized trials designed to test theory-based engagement strategies within a real-world DMH platform where disengagement can occur within seconds. Results will identify which strategies show promise for improving naturalistic engagement among MHA's SGM visitors and inform future refinement of engagement strategies and adaptive decision rules for optimizing engagement with DMH resources.