RecruitingEarly Phase 1Drug trialEffects of Dronabinol in Opioid Maintained PatientsTwenty male and female (ages 18-70) participants with OUD currently receiving methadone or buprenorphine will be enrolled. Prior to their daily methadone or buprenorphine dose and thus at trough plasma levels of opioid, participants will receive dronabinol (2.5 mg, 5mg) or placebo. Subsequently, all participants will undergo laboratory testing of opioid-related outcomes. Pain sensitivity will be measured using a technique called the (QST) quantitative sensory testing, which involves the administering heat or cold stimulation. A Short-Form McGill Pain Questionnaire (SF-MPQ) and a pain Visual Analog Scale (VAS). Attentional bias will be measured using a visual probe task. Negative affect will be measured using the Positive and Negative Affect Schedule (PANAS). Cognitive performance will be measured by a comprehensive cognitive battery. The order of study medication administration will be counterbalanced order to minimize carryover effects. On the initial screening day and at the end of medication treatment, blood will be drawn to determine serum cytokine levels. One week after the last study medication dose, a follow-up session will be conducted during which participants will undergo urine toxicology testing and a safety evaluation before final discharge from the study.