There will be 400 adults with moderate or severe methamphetamine use disorder randomized into this multi-site study. Eligibility will be determined during a maximum 21 day screening period. After screening is completed and eligibility is confirmed, including successful administration of a naloxone challenge, participants will begin the 12 week medication phase of the trial. Participants will be randomized to either the 1) AMC arm and receive injections of extended release naltrexone (XR-NTX; as Vivitrol®) plus once-daily oral extended-release bupropion tablets (BUP-XL) or the 2) matching placebo (PLB) arm and receive injections of placebo (iPLB) plus once-daily oral placebo (oPLB) tablets. During the course of the study, participants may be switched to another arm, as determined by the a priori adaptive aspect of the study design. Participants appearing to respond well to their original treatment assignment will not be switched. Overall, approximately 50% of the participants will receive the AMC. Injections will be administered every three weeks, in weeks 1, 4, 7, and 10. Take-home oral study medication (BUP-XL or oPLB) will be dispensed weekly for dosing on non-clinic days. Participants will be asked to attend the clinic twice weekly for observed oral medication dosing, assessments, collection of urine samples, and once-weekly medical management. On non-clinic days, participants will participate in smartphone app-based medication adherence activities. Participants will be asked to complete assessments as indicated on the schedule of assessments. Following the 12 week medication phase, participants will complete a follow-up phase, including a medication taper and post-medication phase follow-up visits during weeks 13 and 16.

Stage 1 will include 20 individuals with severe stimulant use disorder (methamphetamine type) enrolled across three study sites. Following a maximum 30-day screening period to establish eligibility, participants will receive a monthly injection of extended-release depot naltrexone (XR-NTX; as Vivitrol®) plus once-daily bupropion extended-release tablets (BRP; as Wellbutrin XL®) for 8 weeks. Take-home oral study medication (BRP) will be dispensed weekly for dosing on non-clinic days. Participants will be asked to attend clinic twice weekly for observed BRP dosing, collection of urine samples, assessments, and medical management. Following the 8-week active medication phase, participants will complete a follow-up phase, including a medication taper and post-medication phase follow-up visit during Week 9. If Stage 1 data document success (see criteria below) in at least 3 "responder" study participants, Stage 2 will follow utilizing the same protocol as in Stage 1, to enroll an additional group of 29 participants. Using the same criteria of "responder" success, if the combined stages document success in at least 9 of 49 study participants, the combination medication will be considered to have shown sufficient potential to advance to a large-scale placebo-controlled trial.