PROJECT SUMMARY/ABSTRACT An unprecedented number of new policies across the US threaten the rights of lesbian, gay, bisexual, and transgender (LGBT) populations. In 2023, >500 discriminatory LGBT bills were introduced in state legisla- tures—four-times more than in recent years. Such bills include those banning access to healthcare for trans- gender individuals and those criminalizing teachers for discussing the existence of LGBT people. Emerging data reveal that 70% of LGBT people report discriminatory bills adversely impact their mental health, even when the bills do not become law. Before this rapid increase in discriminatory policies, LGBT people were dis- proportionally burdened by adverse health outcomes, particularly mental health outcomes. The growing threat and enactment of discriminatory LGBT policies will likely widen these disparities. However, little is known about how the recent onslaught of discriminatory LGBT bills collectively influences mental health, particularly in ado- lescence and young adulthood when mental health problems typically onset and when health service use tra- jectories are often established. Without this time-sensitive research, we cannot evaluate the impact of real- world policy environments and address the potential health effects of these discriminatory policies. Informed by the Minority Stress Model, the proposed project's objective is to elucidate how mental health during the critical years of late adolescence and early adulthood (ages 18–24 years) is influenced by four types of LGBT-target- ed policies: 1) religious exemptions, 2) gender-affirming healthcare bans, 3) LGBT-restrictive school curricula, and 4) LGBT-supportive school curricula. To substantiate the link between policies and mental health, we will use a multi-method approach. In the R61 phase, we will collect time-sensitive survey data in the national Healthy Minds Study—the largest ongoing survey of mental health in US colleges and universities—to quantify associations among these policies, enacted stigma (e.g., discrimination, bullying, harassment), and mental health among young adult college students (predicted N=80,850 students at 105 institutions, including four- year schools, community colleges, and minority-serving institutions). In the R33 phase, we will use our newly collected Healthy Minds Study data to identify individuals directly impacted by these policies, with whom we will conduct in-depth qualitative interviews (n=120). To understand the population-level impact of these policies and their mechanisms, we will then use nationally representative data from the Behavioral Risk Factor Surveil- lance System (BRFSS, N=89,493 young adults) to evaluate the impact of LGBT-targeted policies. We will lev- erage quasi-experimental methods (i.e., difference-in-differences analyses) to quantify the causal effect of LGBT-targeted policies as well as causal mediation analyses informed by multi-method results from Aims 1 and 2. This project will ...