Project Summary Transition-age (TA) adulthood—between ages 18 to 25—is a distinct and critical developmental period where unique biological, psychological, and social changes are occurring. Brain development continues into the latter part of this period, with neurological structures associated with reward sensitivity and self-regulation continuing to form. Social roles are in flux, with reduced parental monitoring and shifts in societal expectations that presage lifetime functioning at the personal, familial, and community levels. Substance use disorders (SUD) and mental health conditions are more prevalent in this age group than at other ages, 14.4% and 29.4% respectively in 2019. 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. Although the most efficacious treatment for OUD is pharmacotherapy, naturalistic studies demonstrate that there are large gaps in receipt of medications for opioid use disorder (MOUD), low adherence to these medications, and poor outcomes for most TA adults who enter treatment. Few current studies of quality in OUD treatment programs account for individual, organizational, and contextual factors that vary over time. In particular, variation in the quality of treatment programs occurs within the complex interplay of social and ecological factors related to communities, treatment programs, and characteristics of the patient. Specifically, social determinants of health, such as poverty and racial/ethnic disparities, create added barriers to obtaining and sustaining scientifically supported treatments. A better understanding of the program characteristics associated with higher quality care for TA adults with OUD will inform organizational changes, payer incentives, and government policies to improve treatment for this poorly served population. Because of rapid organizational changes caused by the COVID-19 public health emergency, there is an opportunity to explore whether new forms of SUD treatment delivery—telehealth, liberalization in provision of pharmacotherapy—lead to improved treatment engagement and outcomes for TA adults. The proposed longitudinal study will combine 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) access to MOUD; 2) adherence to pharmacotherapy and retention in treatment; and 3) adverse events (e.g., overdoses). To guide our study, we propose a conceptual model that draws from the Donabedian quality of care framework (Organizational Structure>Clinical Process>Outcome) and from social ecology to examine prog...