Biased Opioid Agonists for Treatment of Opioid Withdrawal in OUD

Background: People with opioid-use disorder (OUD) might benefit from having more treatment drugs to choose from. A new drug, TRV734, could be used like methadone to treat OUD. It might not have as many side effects. Objective: To test if TRV734 relieves withdrawal symptoms and has fewer side effects than oxycodone in people with OUD. Eligibility: People ages 18-75 who have been receiving daily treatment with methadone for opioid use disorder for at least three (3) months Design: Participants will be screened under Protocol 415. They will be screened with: * Medical, social, and psychiatric history * Physical exam * Electrocardiogram (ECG): For this, sticky pads will be placed on the participant's chest to monitor their heartbeat. * Blood and urine tests Participants will stay in a residential unit for 13-21 days. Most days, participants will receive their regular daily dose of methadone. On 4 or 5 occasions, 3-4 days apart, participants will skip two doses of methadone in a row. About 4 hours after they skip the second dose, they will have an IV catheter inserted with a needle so that blood samples can be taken. They will take capsules of either oxycodone, a placebo, or the study drug. They will have an ECG. They will complete questionnaires. Their blood pressure, pupil size, and alertness will be tested. They will then take their usual dose of methadone. Participants will give daily urine and breath samples.