PROJECT SUMMARY/ABSTRACT Sexual and gender minority youth (SGMY; e.g., lesbian, gay, bisexual, transgender, and nonbinary people <18 years) experience substantial inequities in alcohol use, thus placing SGMY at greater risk for alcohol-related morbidity and mortality across the life-course. Despite making great strides in identifying determinants (e.g., minority stress and discrimination) of these inequities over the last 25 years, evidence-based interventions for reducing SGMY alcohol use are lacking. Our primary objective for this application is to rigorously test the efficacy of Singularities, a theory-based, SGMY-informed, game-based intervention for preventing and reducing SGMY binge drinking. This game was developed and pilot tested in our previous grant (R21HD083561; PI: Egan), which showed that the game was highly acceptable to SGMY and had preliminary efficacy for reducing SGMY’s binge drinking frequency. Our proposed fully-powered efficacy trial is the next step to confirm the public health impacts of our game-based intervention. In Aim 1a, we will conduct a randomized controlled trial to test the short-term, mid-term, and long-term efficacy of a game-based intervention for preventing and reducing binge drinking among SGMY (n=2,298). We hypothesize that at 3, 6, and 12 months after intervention delivery, SGMY in the game-based intervention arm vs. control arm will have greater reductions in binge drinking (primary outcome) and other health risk behaviors (secondary outcomes). In Aim 1b, we will explore the feasibility of intervention uptake and engagement in a non-randomized non- incentivized SGMY subsample (n=60) to elucidate intervention implementation under real world conditions. In Aim 2, we will quantitatively explore if RCT participants’ baseline minority stressors (across multiple distal and proximal domains) and demographics (e.g., race/ethnicity) interact with the intervention to predict changes in binge drinking and other outcomes (i.e., how intervention efficacy differs by subgroups). In Aim 3, we will qualitatively explore (via post-RCT interviews) the interplay between intervention participants’ binge drinking, minority stressors, and their use of game-based skills. Upon successful completion of this research, the expected outcome is to have an evidence-based intervention for significantly reducing SGMY binge drinking. Further, our study will provide mixed methods results identifying how minority stress and demographics moderate the efficacy of our evidence-based intervention, which will inform the field about for whom SGMY- affirmative interventions are most beneficial and illuminate for whom additional interventions are needed. These results will have positive impacts because our intervention has potential to be widely scaled via online dissemination and can help federal agencies meet their goals (e.g., Healthy People 2030) of reducing population-level SGMY inequities in alcohol use.