Impulsivity and Stimulant Administration

Inclusion Criteria: 1. age 18 - 50 years, 2. voluntary, written, informed consent, 3. physically healthy by medical history, physical, neurological, ECG, and laboratory examinations, 4. DSM-IV criteria for Cocaine Abuse (305.60) or Cocaine Dependence (304.20) 5. recent street cocaine use in excess of amounts to be administered in the current study, 6. intravenous and/or smoked (crack/ freebase) use, 7. positive urine toxicology screen for cocaine, 8. for females, non-lactating, no longer of child-bearing potential (or agree to practice effective contraception during the study), and a negative serum pregnancy (β-HCG) test. Exclusion Criteria: 1. Other drug dependence (except nicotine) as determined by urine toxicology or interview 2. \< 1 year of cocaine dependence, 3. a primary major DSM-IV psychiatric diagnosis (schizophrenia, bipolar disorder, etc.), unrelated to cocaine, 4. a history of significant medical (cardiovascular) or neurological illness, ie prior myocardial infarction, current active symptoms of cardiovascular disease / angina, evidence of cocaine-related cardiovascular symptoms, prior arrhythmias or need for cardiovascular resuscitation, neurovascular events such as transient ischemic attacks, stroke, and/or seizures Parameters re: elevations in vital signs are now explicitly specified under "Safety features built into our one-day self-administration paradigm). 5. current use of psychotropic and/or potentially psychoactive prescription medication, 6. seeking treatment for drug abuse/dependence (for experimental cocaine component), 7. physical or laboratory (β-HCG) evidence of pregnancy. 8. current use of any medication (prescription or over-the-counter) determined to cause potential drug interactions by the study physicians.