PROJECT ABSTRACT People who inject drugs (PWID) are less likely to maintain viral suppression, perpetuating HIV transmission among PWID over the past two years in Massachusetts. While resource intensive intervention strategies (i.e., incentive-based interventions and directly observed therapy (DOT)) have demonstrated effectiveness for improving ART adherence in the short-term, they do not address underlying barriers to engagement in HIV care for PWID, such internalized and anticipated stigma. Acceptable, feasible, and scalable intervention strategies that combine these intervention strategies with an evidence-based cognitive behavioral therapy (CBT) intervention designed to address internalized and anticipated stigma related to substance use, as well as other related stigmas (e.g., HIV) and their sequelae (e.g., avoidance behaviors) optimized for PWID may result in sustained adherence and viral suppression over time. We hypothesize that combining an app-based video-delivered optimized stigma-focused CBT intervention coupled with app-based video-delivered short-term incentivized DOT will have longer lasting effects than short-term incentivized DOT alone. To test this hypothesis, data on the feasibility, acceptability, and scalability of a combined intervention, optimized for PWID, is needed. In this R34 we will leverage the multiphase optimization strategy (MOST) to facilitate the optimization of an evidence-based video-delivered stigma-focused CBT intervention for PWID living with HIV in Massachusetts who are not virally suppressed (aim 1). We will then utilize implementation science strategies in a Hybrid Type 1 design to simultaneously conduct a pilot randomized controlled trial (RCT) to test the feasibility and acceptability of the optimized stigma-focused CBT intervention paired with incentivized DOT compared to incentivized DOT alone, both implemented through a tailored mobile app (emocha®; n=70; aim 2), while rigorously testing the implementation strategy, including scalability (aim 3). By accomplishing these aims, we will develop and refine critical components of the intervention, including optimizing the stigma-focused CBT intervention and assessing the acceptability, feasibility, and preliminary scalability of combined intervention. This R34 will enable the development and refinement of the infrastructure for a fully powered RCT, which will be submitted as a subsequent R01 to test the effectiveness of the intervention and scalability. Throughout this R34 and the subsequent R01, we will work closely with the Massachusetts Department of Public Health, given their interest in implementing this intervention strategy and platform should it be identified as effective and scalable.