The purpose of this study is to see if brenipatide, when compared to placebo, is safe and effective for participants with opioid use disorder, when used with buprenorphine with or without naloxone. The maximum potential duration of study participation for a participant in Part A is approximately 144 weeks, maximum potential duration of study participation for a participant in Part B is approximately 116 weeks. The actual duration will vary for each participant depending on the time of enrollment and the overall rate of study enrollment.