PROJECT SUMMARY/ABSTRACT Young adults have rising rates of opioid-related morbidity and mortality, and those who inject opioids are a particularly vulnerable group. Infectious bacterial complications of injection drug use (IC-IDU) contribute to high morbidity and mortality and lead to lengthy hospitalizations for severe infections, such as endocarditis and osteomyelitis. Despite evidence showing receipt of medications for opioid use disorder (MOUD) can reduce opioid-related mortality and that initiation of MOUD during hospitalization leads to improved engagement in OUD treatment at discharge, only a minority of patients receive MOUD during hospitalization. Untreated substance use in young adults hospitalized with IC-IDU leads to readmissions, high medical costs, and recurrent infections. As a health services researcher and specialty-trained physician in adolescent and addiction medicine, I am well trained to identify the health needs of this population and to not only design effective interventions, but to translate them into clinical practice. The overall objective of this application is to develop a clinician-facing intervention to improve delivery of MOUD to hospitalized young adults with IC-IDU. Specific aims include: 1a) Identify multi-level barriers and facilitators that may influence the delivery of MOUD during hospitalization, by conducting semi-structured qualitative interviews with the following stakeholders: clinicians, hospital social workers/case managers, and young adults. 1b) Use intervention mapping to systematically develop a clinician-facing intervention. We will build on components of an existing outpatient intervention to develop a multi-component, inpatient clinician- facing intervention to improve delivery of MOUD. 2) Pilot test a clinician-facing intervention to improve delivery of MOUD. The intervention will focus on changing clinician behavior and addressing key patient, provider and system-level barriers to improve hospital prescription of MOUD and linkage to outpatient OUD treatment. Our primary outcomes will include feasibility and acceptability. An acceptable and feasible health system intervention to improve delivery of MOUD to young adults with OUD and IC-IDU would address a profound public health crisis. Our aims will identify best practices for recruitment and retention, support development and testing of study measures, and identify potential difficulties in delivery of the intervention bundle. This will lead to a R01 hybrid effectiveness-implementation trial to test the impact of the intervention and supportive implementation strategies in multiple clinical sites. This award will allow me to become an independent clinician-investigator in health services research and implementation science.