On day 5, the challenge dose of 0.2 or 3.6. mg of oral buprenorphine (Temgesic, Schering-Plough) will be administered at 11.00, i.e. 1 h after the last dose of placebo or voriconazole. The dose is 3.6 mg after placebo and 0.2 mg after voriconazole. If necessary, naloxone (Naloxone B. Braun, Braun) will be given in sufficient doses to counteract the severe adverse effects of buprenorphine. For nausea and vomiting, intravenous tropisetron will used, if needed.