PROJECT SUMMARY/ABSTRACT: Two-thirds of individuals with opioid use disorder (OUD) first misuse opioids before age 25. Intervention early in the life course is critical, and requires that adolescents and young adults (hereafter, “youth”) receive high- quality care in a continuum of care. Optimizing clinical care at every stage in this continuum is critical, and cannot be achieved alongside persistent racial and ethnic disparities. To lay the groundwork for quality improvement nationwide in Medicaid programs—the primary insurers for youth of color in the US—this project will apply the Cascade of Care framework to OUD identification and treatment in youth. The Cascade describes a series of 5 stages, i.e., how many youth with OUD (i) are identified (“diagnosis”), (ii) begin treatment (“initiation”), (iii) start medications for opioid use disorder (“MOUD”), (iv) stay in treatment in the short-term (“engagement”), and (v) stay in treatment in the long term (“retention”). Analyses will use newly released Medicaid data from across US states linked to numerous national databases to provide key county- and state-level information. The central objective is to provide a comprehensive picture of the Cascade for youth aged 13-25 with OUD, throughout focusing on disparities. Specific Aims are to: (1) Apply the Cascade of Care framework to youth with OUD and estimate racial and ethnic disparities at each stage, using a systematic approach to uncover underlying, potentially intervenable mechanisms contributing to disparities; (2) Determine whether MOUD receipt is associated with subsequent treatment engagement and retention, and with smaller racial and ethnic disparities, thus informing whether MOUD might be a strategy to reduce inequities in OUD treatment; and (3) Determine whether the Cascade is associated with emergency department use and hospitalizations, thus identifying whether real-world clinical outcomes worsen when youth leave the Cascade, and whether such outcomes are disproportionately experienced by youth of color. Throughout, race is conceptualized as a social (not biological) construct, and the project seeks to identify ways that the operation of healthcare systems and legal and regulatory climates contribute to health disparities, in order to ultimately guide policy change. The research team brings together expertise in youth, OUD treatment, health disparities, community engagement, health services research, and relevant statistical approaches. The project will be guided by a diverse Youth and Family Advisory Board to inform protocol development, analysis, interpretation, and dissemination of findings, with a goal of maximizing relevance and delivery of results to youth and families, as well as key stakeholders nationally.