Rapid Outpatient Low-dose Initiation of Buprenorphine for OUD With Fentanyl Use

Inclusion Criteria: * Ages 18 or older * Male, female, transgender, or non-binary * DSM-5 criteria for opioid use disorder, moderate to severe * Fentanyl positive on urine drug test * Able to provide written informed consent in English prior to any study-related procedure Exclusion Criteria: * Pregnancy or actively lactating * Previously documented hypersensitivity or allergy to buprenorphine or naloxone * DSM-5 criteria for substance use disorder other than opioid use disorder (e.g., cannabis, cocaine, alcohol) * Current benzodiazepine use * Urine drug testing at screening positive for buprenorphine and/or methadone * AST and/or ALT \>3x upper limit of normal or total bilirubin \>1.5x upper limit of normal * eGFR \<30 mL/min * Use of CYP3A4-metabolized agents such as azole antifungals, macrolides, and protease inhibitors * High risk of severe medetomidine withdrawal based on drug urine testing for medetomidine, prior withdrawal syndrome requiring intensive care unit admission, and/or patient-reported severe nausea/vomiting during early withdrawal, at the discretion of the study physicians. * Significant medical symptoms (e.g. severe respiratory insufficiency), psychiatric symptoms, or dementia that, in the opinion of the investigators, would preclude compliance with the protocol, cooperation in the study, obtaining informed consent, or ability to safely participate in the study * Pending legal action that could prohibit participation and/or compliance in study procedures