PROJECT SUMMARY/ABSTRACT Of the nearly 400,000 people with an opioid use disorder (OUD) who receive OUD treatment each year, 1 in 6 utilize residential services. Community re-entry after residential OUD treatment is an especially vulnerable time, with most people who return to use doing so in the 30 days following discharge. Posttraumatic stress disorder (PTSD) is highly prevalent (>50%) among people in residential OUD treatment and linked to worse opioid outcomes following treatment, including return to use during community re-entry. However, while PTSD treatment access high-risk the they access individual is safe/acceptable/efficacious for people with OUD, return to use after residential OUD treatment happens so quickly, it is critical that patients have to empirically-supported tools that deliver ongoing upport and resources for PTSD-OUD during this transitional period. Rigorously-developed mobile ealth interventions that adapt provision of care to individual offer a promising and innovative approach to continuing care after residential OUD treatment: can be easily disseminated o people from a wide demographic (high scalability), ensuring equitable to OUD care for our most marginalized populations; overcome many of the structural, social, and barriers to traditional treatment; are cost-effective and sustainable; and provide personalized 24/7 OUD programs rarely provide PTSD treatment. Because s h t care to people at their moments of greatest need while maintaining standardization and fidelity of treatment. The proposed study will use a ground-up approach to rigorously develop and evaluate a mobile app with both on-demand (24/7 PTSD-OUD resources) and automated (skills-based PTSD-OUD interventions) features to reduce opioid use/harms during community re-entry of adults with co-morbid PTSD-OUD. Aim 1 will use ecological momentary assessment (EMA) to identify tailoring of Aim variables (i.e., states of high risk for occurrence opioid use and related harms) for a just-in-time adaptive intervention (JITAI) component of the mobile app. 2 will experimental design to ruse a hybrid igorously develop and evaluate the mobile app. Specifically, microrandomized trial (MRT) will evaluate the efficacyof intervention options (JITAI) vs. generic reminders to access resources on the proximal occurrence of opioid use and harms, including optimization of decision rules (e.g., when, whether) to alter dosage, type, and timing of JITAI intervention option delivery, and controlled secondary Our final community Such randomized trail (RCT) will provide an initia l test of efficacy (primary outcomes: r eturn to opioid use and harms; outcome: PTSD severity) and implementation outcomes of mobile app vs. treatment-as-usual. product will be a highly scalable mobile app that provides access to 24/7 continuing care during re-entry (on-demand resources), including in xact moments of need (skills-based interventions). a clinical tool has strong potential to improve health and quality of life for individuals with PTSD-OUD. e

PROJECT NARRATIVE Community re-entry is disorder following residential opioid use disorder (OUD) treatment is a critically vulnerable time that characterized by high rates of return to use, particularly for individuals with co-morbid posttraumatic stress (PTSD). This proposal willuse a ground-up approach to rigorously develop and evaluate a mobile app with both on-demand (24/7 PTSD-OUD resources) and automated (skills-based PTSD-OUD interventions) features to reduce opioid use/harms during community re-entry of adults with co-morbid PTSD-OUD. Our final productwill be a highly scalable mobile app that has strong potential to improve health and quality of life.