Onsite PTSD Treatment to Improve MOUD Outcomes (OPTIMO): a hybrid Type 1 effectiveness-implementation trial of PTSD care in community-based settings that serve people who use drugs - Our goal is to improve opioid use disorder (OUD) treatment engagement and effectiveness for people who inject drugs (PWID) with co-occurring posttraumatic stress disorder (PTSD). Medications for opioid use disorder (MOUDs) such as methadone and buprenorphine are effective but retention in treatment is suboptimal. For PWID, PTSD is exceedingly common (25-50%), intensifies illicit opioid use, doubles overdose likelihood, and increases risk of HIV/HCV infection. Because PTSD is a modifiable risk factor for negative OUD outcomes, reducing PTSD symptom severity can improve emotional regulation, and help PWID stay retained to lifesaving MOUDs. In collaboration with three community-based organizations that serve PWID, we propose to adapt Cognitive Processing Therapy (CPT), an evidence-based PTSD treatment, for the unique needs of PWID with PTSD. Adapting CPT for the OUD population will allow us to reach PWID who have high rates of chronic PTSD, infrequently use conventional healthcare settings, and experience severe OUD-related harms. Onsite PTSD Treatment to Improve MOUD Outcomes (OPTIMO) will be an innovative model of CPT, whereby flexibly dosed CPT will be delivered via telehealth at the community-based organizations and staff “coaches” provide additional in-person support. Our study team has a proven track record of collaborating with community-based organizations to provide onsite low-barrier MOUDs, working with PWID who have PTSD, and successfully adapting CPT to low resource, high adversity contexts, co-occurring substance use disorders, and telehealth delivery. In R61 Aim 1, we will adapt CPT for PWID. Guided by CDC’s framework for systematic intervention adaptation and Consolidated Framework for Implementation Research, our modified CPT protocol will be tailored through: 1) input from a stakeholder advisory board and 2) feedback from potential consumers and SSP staff (6 focus groups; n = 4-6). Subsequently, in R61 Aim 2, we will preliminarily test and refine OPTIMO’s acceptability and feasibility by conducting a one-armed open trial (n = 15) and collecting outcome and process measures from participants, teleproviders, and staff “coaches.” Upon meeting R61 milestones of demonstrated feasibility and acceptability, we will conduct a hybrid Type 1 effectiveness- implementation trial: we will enroll 252 individuals with co-occurring OUD and PTSD and randomize 1:1 to OPTIMO or wait-list control, comparing treatment effects on PTSD symptoms, MOUD retention, opioid use, and injection-related risks (R33 Aim 1). To inform future scaling efforts, we will systematically evaluate OPTIMO’s reach, adoption, implementation, and anticipated maintenance and their determinants through interviews with participants, providers, and community-based organization leadership (R33 Aim 2). Completing these aims will lead to more optimal integration of mental health care and MOUDs in a community-based setting to better retain a high-risk population of PWID, thus reducing the toll of untreated OUD.