Stimulant drug (e.g., crystal methamphetamine, cocaine, ecstasy, MDMA) use is a substantial public health problem among young gay, bisexual and other men who have sex with men (YGBMSM) in the United States (US). Stimulant use is associated with increased engagement in sexual risk behaviors and decreased use of HIV prevention and treatment services, and as such leads to increased HIV acquisition/transmission. There are currently no evidence-based interventions to reduce stimulant use and concurrent HIV risk among YGBMSM; in response to this urgent need and building of over a decade of NIH-funded formative and pilot research, the proposed hybrid type 2 effectiveness-implementation trial is designed to assess the effectiveness and implementation strategies of Project IMPACT—a HIV status neutral, modular behavioral intervention to reduce HIV risk in YGBMSM who use stimulants in the context of high-risk sex. The intervention incorporates HIV risk reduction counseling (including supporting PrEP and ART use) with behavioral activation (BA)—an evidence-based, easy to administer, cognitive behavioral approach to treat depression that focuses on helping individuals re-engage in activities that generate feelings of enjoyment. Our conceptual model posits that BA will re-engage YGBMSM in pleasurable non-drug use activities that will serve as a natural reinforcement for functional behavior, improve depressed mood when not on stimulants by experiencing increases in pleasure, and decrease overall distress so that YGBMSM who use stimulants can better benefit from HIV risk reduction counseling. The initial pilot trials of Project IMPACT resulted in significant reductions in sexual risk, stimulant use and depressive symptoms. Research Plan Overview: By harnessing the resources, geographic and site diversity, and multidisciplinary expertise of the Adolescent Trials Network (ATN), the current proposal aims to efficiently and rigorously prepare Project IMPACT for rapid translation into real-world practice. Following the RE-AIM Framework, we will test the reach and effectiveness of Project IMPACT (compared to an enhanced Standard of Care condition) in a two-arm, multi-site and multi-format (i.e., in-person and virtual) randomized controlled trial of 360 cisgender YGBMSM who use stimulants in the context of high-risk sex. Participants will be followed for 12 months, and primary outcomes include number of condomless anal sex acts while not protected by PrEP (HIV- YGBMSM) or while not virally suppressed (HIV+ YGBMSM) and stimulant use (via urinalysis). We will also test our multi-faceted implementation strategy by assessing adoption/ accessibility and implementation using mixed-methods assessments that describe and examine characteristics of successful implementation (including differences by intervention delivery format). Finally, we will assess the feasibility of maintenance and sustainment of Project IMPACT by using the well-established CEPAC-AYA model to project its cost effectiveness on HIV transmissions, QALYs, and per person lifetime costs.