Inclusion Criteria:  Males and females between 18 - 65 years-of-age; Understand the study procedures and provide written informed consent in English language; Meet current DSM-5 criteria for opioid use disorder, of at least moderate severity, currently engaged medication assisted treatment at a buprenorphine-naloxone sublingual film daily dose ranging from 8mg/2mg to 24mg/6mg or buprenorphine sublingual tablet 5.7mg/1.4mg to 17.1/4.3 once daily for at least last 2 weeks; Have a positive urine drug screen for buprenorphine during screening and on admission to the clinical research unit to document buprenorphine use; Have a Pittsburgh Sleep Quality Index (PSQI) Total Score of 6 or higher.  Exclusion Criteria:  Contraindications for participation as determined by medical history and physical exam performed by study NP or study physician; Pregnant or nursing women; Baseline ECG with clinically significant abnormal conduction; Uncontrolled serious psychiatric or major medical disorder, including COPD. Narcolepsy is also considered exclusionary; Taking prescription or over-the counter drugs or dietary supplements known to significantly inhibit CYP3A4 (such as Clarithromycin, telithromycin, nefazodone, itraconazole, ketoconazole, atazanavir, darunavir, indinavir, lopinavir, nelfinavir, ritonavir, saquinavir, tipranavir), or CYP3A4 inducers (such as phenobarbital, phenytoin, rifampicin, St. John's Wort, and glucocorticoids); Prescribed medications for insomnia, or unable to discontinue over the counter drugs or dietary supplements used to treat insomnia on study days. Current severe alcohol use disorder or current benzodiazepine use disorder Current DSM-5 diagnosis of any psychoactive substance use disorder other than opioids, cocaine, marijuana, or nicotine, or mild or moderate alcohol use disorder. Diagnosis of mild to moderate use disorder for alcohol will not be considered exclusionary. Any previous medically adverse reaction to opioids or lemborexant: Significant current suicidal or homicidal ideation (C-SSRS "yes" answers on questions 4 or 5) or a history of suicide attempt within the past 6 months. Subjects with Suicidal Behaviors Questionnaire-Revised score ≥8 at the screening visit. Any other severe acute or chronic medical or psychiatric condition or laboratory abnormality that may increase the risk associated with study participation or investigational product administration or may interfere with the interpretation of study results and, in the judgment of the investigator, would make the subject inappropriate for entry into this study.