- 1. Meet DSM IV criteria for cocaine dependence; 2. Have a self-reported history of using cocaine by the smoked or IV route. Participants must report at least weekly use for the past month and have a cocaine-positive urine test in the week of study entry; 3. Have vital signs after a 48 hours washout period as follows: resting pulse between 50 and 80 bpm, blood pressures between 105-130mm Hg systolic and 45-80mm Hg diastolic; 4. Have hematology and chemistry laboratory tests that are within normal (+/- 10%) limits with the following exceptions: a) liver function tests (total bilirubin, ALT, AST, and alkaline phosphatase) < 3 x the upper limit of normal, and b) kidney function tests (creatinine and BUN) < 2 x the upper limit of normal; 5. Have a baseline ECG that demonstrates normal sinus rhythm, normal conduction, and no clinically significant arrhythmias; and 6. Have a medical history and standard physical examination demonstrating no clinically significant contraindications for study participation, in the judgment of the admitting physician and the principal investigator.