PROJECT SUMMARY Morbidity and mortality related to opioid use continue to rise, with fentanyl now the most common opioid involved in overdose death. Despite three FDA approved medications for opioid use disorder (MOUD)—methadone, buprenorphine, and naltrexone--as many as 3 out of 4 people with OUD are not on any of these lifesaving medications, which speaks to failures in implementation. The penetration of fentanyl into the opioid supply has made strategies for initiation of buprenorphine even more complex. Growing literature describes increased precipitated withdrawal at the time of buprenorphine initiation, thought to be secondary to the lipophilic nature of fentanyl. There is an urgent need to better understand how we can successfully engage more people in treatment that we know decreases morbidity and mortality related to OUD. The work proposed in this K23 application will investigate the initiation of buprenorphine in the setting of fentanyl use from both the patient and provider perspectives. We will utilize novel methods to develop a buprenorphine initiation toolkit and then will pilot the implementation of this new tool. The specific aims of the research are to: 1. Use qualitative methods to explore the experience of both patients and providers initiating buprenorphine for OUD in the setting of fentanyl use. 2a. Conduct a modified Delphi process to investigate expert consensus regarding buprenorphine initiation in the setting of fentanyl. 2b. Work with a multidisciplinary group to develop a buprenorphine initiation toolkit, and 3: Conduct a pilot study to evaluate the acceptability, feasibility and effectiveness of the buprenorphine initiation toolkit. Along with the multipronged training plan, this research will support my overarching goal of becoming an independent physician researcher focused on improving outcomes for people with substance use disorders through innovative implementation approaches.