PROJECT SUMMARY The parent grant for this supplement explores variation in quality of care for transition age adults with opioid use disorder. TA adulthood—between ages 18 to 25—is a distinct and critical developmental period where unique biological, psychological, and social changes are occurring. SUD and mental health conditions are more prevalent in this age group than at other ages. Effective treatment at this age has the potential for large long-term payoffs. Over the past decade, there has been a large rise in the prevalence of opioid use disorders (OUD) among TA adults. Yet, the treatment system for OUD performs poorly for TA adults: they are less likely to obtain scientifically supported treatment and more likely to leave treatment early. The parent study combines data from multiple sources, including Medicaid and a state registry of SUD treatment episodes, to examine three aspects of OUD treatment quality for approximately 65,000 TA adults entering treatment for OUD between 2012 and 2025: 1) MOUD use; 2) adherence to pharmacotherapy and retention in treatment; and 3) adverse events (e.g., overdoses). To guide our study, we employ a conceptual model that draws from the Donabedian quality of care framework (Organizational Structure>Clinical Process>Outcome) and from social ecology to examine program quality of OUD treatment for TA adults while accounting for individual and community level factors associated with the ability of these programs to deliver care. An important feature of this project is the close partnership between the academic research team and leadership for the agency that regulates addiction treatment in New York. Mr. Rentería’s professional development will be enhanced by participating in this partnership between health services researchers and policy makers to bring scientific methods to practice change. Current progress. The parent award is in its first year of a five-year project. The multidisciplinary and cross-institutional project team has formed, the analytical dataset is being developed, and outreach has begun to develop and convene a stakeholder council to advise on the conduct of the research. One emerging question stemming from early meetings of the investigative team is about variation in beliefs, values, and practices of prescribers of MOUD for TA adults. The decisions regarding medication administration among these prescribers may have significant impact on the response to treatment among TA adults.