Effects of Lemborexant on Insomnia and Its Relationship to Mood and Behavior on Opioid Use Disorder Subjects

The goal of this clinical trial is to learn about how certain medications used to treat insomnia (e.g., Lemborexant) impact sleep, mood, and behavior in men and women with Opioid Use Disorder who are taking prescribed buprenorphine. The main questions it aims to answer are: 1. What is the effect of the study drug (lemborexant) on sleep outcomes? 2. What is the effect of the study drug (lemborexant) on impulsive behavior (as measured by computer test performance)? 3. What is the effect of the study drug (lemborexant) on mood and other behavior? Researchers will compare lemborexant to placebo (e.g., sugar pill) to see if participants assigned to 8 weeks of treatment with lemborexant have greater improvements on the measures listed above. Participants will take the study medication (or placebo) each night for 8 weeks and be asked to come for a total of 23 study visits. Most of these visits will be very short (15-30 minutes). The longer visits will include the screening visit (about 2-3 hrs), baseline visit (about 2.5 hrs), and the post-medication visit (about 2 hrs). Study visits will include things like taking surveys about sleep, drug use, and mood, completing urine drug testing, checking vital signs (e.g., blood pressure), and completing interviews with the study staff. Participants will also be asked to provide two blood samples (one during screening and one after taking the medication). For three two-week periods, participants will be asked to wear a watch to track sleep at home, and to keep a log of sleep and wake times.