Office-based Methadone Versus Buprenorphine to Address Retention in Medication for Opioid Use Disorder Treatment.

Inclusion Criteria * 18 years of age or older; * Meet Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) criteria for OUD; * Are initiating a new MOUD treatment episode Exclusion Criteria * Have been prescribed (and ingested) or been administered more than 72 hours of MOUD in the 7 days prior to randomization as a "bridge" to the new OUD treatment episode. Such MOUD may include prescribed (and ingested) or administered medically managed withdrawal (aka detoxification). * Known contraindication to methadone or BUP * Unwilling to pursue or continue pre-natal care or pregnancy counseling if determined pregnant by urine human chorionic gonadotropin (hCG) testing at the screening assessment * Be actively suicidal or severely cognitively impaired (e.g., dementia, untreated psychosis) precluding informed consent as determined by site clinician * Current severe comorbid substance use disorder requiring residential or inpatient treatment services as determined by site clinician * Be unable to provide locator information including one or more contacts in addition to themselves * Be unwilling to follow study procedures (e.g., unwilling to receive treatment from site clinician, use the study pharmacy, unwilling to be randomized to BUP or methadone, or will be unavailable for the follow-up assessments) including allowing the researchers to access their record in the EMR and state's prescription drug monitoring program * Have previously enrolled in CTN-0131 * Currently enrolled in another research study which will conflict with study procedures * Are currently in jail, prison or other overnight facility as required by a court of law or have pending legal action that could prevent participation in study activities * Unable to conduct research assessments in English as determined by Site PI or their designee.