The investigators propose a rigorous, Phase II, three-group, placebo-controlled double-blind randomized controlled trial (RCT) to evaluate the efficacy of buspirone for both withdrawal and craving among individuals with opioid use disorder (OUD) undergoing a standardized stepwise taper. During this 10 to 12-day residential study, participants with OUD will be enrolled, stabilized on a short-acting opioid, undergo an opioid stepwise taper, and complete a post-taper observation period where participants will have the opportunity to initiate long-term buprenorphine or extended-release naltrexone.