PROJECT SUMMARY/ABSTRACT: The goal of this K23 Mentored Patient-Oriented Research Career Development Award is to support the applicant in developing the critical skills necessary to become an expert in increasing access to evidence-based treatment for opioid use disorder (OUD) at touchpoints for care that individuals with OUD are likely to frequent. The proposed research focuses on NIDA's priority area of addressing real-world complexities by developing implementation strategies to improve treatment continuity after hospitalization in patients with OUD. Hospitalizations related to OUD and its complications have increased dramatically over the last few decades, leading to high morbidity, mortality, and healthcare costs. Hospitals are increasingly recognized as critical touchpoints for engaging individuals with OUD in treatment, and randomized controlled trials support the efficacy of initiating medications for OUD (MOUD) in acute care settings to increase treatment engagement following discharge. However, hospital-initiated treatment is insufficient if patients do not continue care in the community. Despite the robust literature on care transitions after hospital discharge for patients with other chronic conditions, there is limited evidence about the best strategies to optimize care engagement for patients with OUD after hospitalization. We need effective, scalable strategies for linking patients with OUD from acute care to ongoing treatment, including continuation of MOUDs. The research objective of this proposal is to develop and pilot test strategies to facilitate transitions of care for patients with OUD from the hospital to the community. The specific aims are: (1) Use a mixed-methods approach to identify determinants of effective care transitions for patients with OUD from acute care to outpatient treatment at the patient, provider, and system level, (2) Partner with hospital and community stakeholders and use implementation mapping to develop a multicomponent, modular toolkit to facilitate transitions from acute care to community addressing multi- level barriers, and (3) Conduct a pilot trial of the care transition toolkit. The primary outcome will be treatment engagement at 30 days, and secondary outcomes will include MOUD and substance use, service use, feasibility, acceptability and patient satisfaction. The mentorship team brings together experts in health services research, implementation science, and care delivery interventions for OUD as well as stakeholder advisors from hospital and community settings. This Mentored Research Scientist Development Award builds on Dr. Lowenstein's experience as a clinician and researcher and extends it with five key training goals: 1) Measuring outcomes for OUD-related care across systems, 2) Advanced qualitative inquiry, 3) Implementing health systems change, and 5) Manuscript and grant writing. With successful completion of this project, training activities, and mentorship from a team of experience...