Subjects will be studied during a maximum of seven occasions.
Study drugs are intravenous buprenorphine (0.025-0.2 mg infused over 1 hr) and sublingual buprenorphine (2-4 mg), with 1-3 week washout between sessions.
Sessions 1\&2: Control (no pretreatment) - intravenous and sublingual buprenorphine. Some subjects will only undergo session 1 (IV)
Sessions 3\&4: Liver and gut CYP3A induction (rifampin 600 mg daily), intravenous and sublingual buprenorphine
Session 5: Gut only CYP3A inhibition (grapefruit juice the night before), sublingual buprenorphine
Sessions 6\&7: Liver and gut CYP3A inhibition (ketoconazole 400 mg daily), intravenous and sublingual buprenorphine
