Suvorexant as an Adjunct to Buprenorphine in Persons Who Use Fentanyl

Inclusion Criteria: * Aged 18-65 * Meets DSM-5 criteria for opioid use disorder (OUD) with evidence of physical dependence on opioids * Provides a urine sample that tests positive for fentanyl and/or fentanyl analogues * Interest in being maintained on buprenorphine for OUD * Plans to reside in current area for study period * Achieving a study maintenance dose of \>=8mg sublingual buprenorphine/naloxone * Willing to comply with study protocol * Have no clinically significant chronic medical or surgical disorders or conditions that are judged by the investigators to prevent participation Exclusion Criteria: * Medically contraindicated for buprenorphine, extended-release (XR)-buprenorphine (Sublocade), or suvorexant (as per medication labels) * Pregnant or breast feeding * Severe Diagnostic and Statistical Manual (DSM)-5 alcohol or benzodiazepine use disorder or evidence of alcohol/benzodiazepine physical dependence * Have a known allergy to the study medications * Past 30-day prescribed use of suvorexant for the indication of insomnia * Current benzodiazepine or other prescribed medication for the indication of insomnia * Urine sample testing positive for benzodiazepine at screening and admission to residential treatment * Current narcolepsy, restless leg syndrome or sleep paralysis * High risk for current sleep apnea * Current (past 30-day) suicidal behaviors * Severe hepatic or renal impairment * aspartate aminotransferase (AST) or alanine aminotransferase (ALT) \>3x upper limit of normal (ULN) * Total bilirubin \>2x ULN * Creatinine \>1.5x ULN * Past year clinically-significant psychiatric condition judged to interfere with study participation * Lack of access to stable housing (necessary for electronic pill dispenser charging) * Have circumstances that would interfere with study participation (e.g., impending jail)