The primary objective of this research study is to evaluate the effect of tirzepatide, relative to placebo, as an adjunct to BUP on retention, substance use, and sleep outcomes in individuals with OUD.

This is a Phase 2, pragmatic, multi-site, double-blind, randomized, placebo-controlled, intent-to-treat trial. The selection of placebo as the comparator is considered the gold standard for medication trials. Eligible participants will be randomized in a 1:1 ratio to tirzepatide or placebo, balancing on site and buprenorphine (BUP) formulation (transmucosal vs extended-release). Participants will receive tirzepatide or placebo based on randomized assignment, with "dose escalation" of placebo following the schedule for tirzepatide and tirzepatide dosing being consistent with prescribing guidelines. Participants will be administered a subcutaneous (SQ) study medication injection weekly and attend weekly research visits through 26 weeks post-randomization with longer research visits at 1, 3, and 6 months post-randomization. A follow-up visit for final safety measures will be completed at week 30, which takes into account tirzepatide's long half-life. Duration of participation will be approximately 31 weeks for study participants. Participants will be administered study medication and attend weekly research visits through 6 months post-randomization with longer research visits at 1-, 3-, and 6-months post-randomization. Participants will be provided with a Fitbit to measure sleep. BUP is not a study medication; participants will receive BUP through their clinical provider. A follow-up visit for final safety measures will be completed at week 30.