Participants will stay on a research ward and will undergo challenge sessions twice per week. The following conditions will be tested: placebo; IM hydromorphone (2 and 4 mg; an opioid agonist positive control condition); SL buprenorphine (4, 8, and 16 mg); IM buprenorphine (4, 8, and 16 mg); SL buprenorphine/naloxone(4/1, 8/2, and 16/4 mg); and IM buprenorphine/naloxone (4/1, 8/2, and 16/4 mg). During challenge sessions, physiological status will be recorded continuously and tasks assessing psychomotor, subjective, and objective status will be performed repeatedly.