 Drug and Doses: Investigators will administer placebo, 0.2 mg and 0.4 mg buprenorphine Temgesic via sublingual tablet in counterbalanced order under double-blind conditions. These tablets dissolve within 5-8 minutes. This drug has been approved for treatment of severe pain. The onset of action after sublingual administration is 30 minutes, with a peak plasma concentration at 15-2 hours and a half-life of 5 hours. These doses of buprenorphine are very low, and the average maintenance dose for opioid abusers is 8 mg. The 0.2-mg dose will help establish a dose-response curve for any effects. Doses will be separated by at least 72 hours. 