Inclusion Criteria:

1. Subjects must be able to provide informed consent and function at an intellectual level sufficient to allow accurate completion of all assessment instruments.
2. Subjects must meet DSM-IV criteria for current cocaine dependence. Subjects may meet criteria for abuse, but not dependence on any other substance with the exceptions of nicotine and alcohol. Because of the high comorbidity of cocaine and nicotine and alcohol dependence, excluding nicotine and alcohol dependence would seriously compromise the feasibility of recruitment. Nicotine use immediately prior to the cue exposure/extinction session will be controlled. Although individuals who meet criteria for alcohol abuse or dependence will be accepted for study participation, anyone who has a measurable blood alcohol level on the day of the sessions will be excluded as acute alcohol intake can increase serum levels of DCS and lower the seizure threshold.
3. Use of one of the following methods of birth control by female subjects: barrier methods (diaphragm or condoms with spermicide or both), surgical sterilization, use of an intra-uterine contraceptive device, or complete abstinence from sexual intercourse.
4. Subjects must live within a 50-mile radius of our research program and have reliable transportation.
5. Subjects must consent to remain abstinent from all drugs of abuse (except nicotine) prior to the first session and through the session on day 5.
6. Subjects must consent to random assignment to the DCS vs. placebo conditions.

Exclusion Criteria:

1. Women who are pregnant, nursing or of childbearing potential and not practicing an effective means of birth control.
2. Subjects with evidence of or a history of significant hematological, endocrine, cardiovascular, pulmonary, renal, gastrointestinal, or neurological disease including diabetes, as these conditions may affect heart rate or skin conductance measurement.
3. Subjects with a history of or current psychotic disorder, current major depressive disorder, bipolar affective disorder or a severe anxiety disorder as these may impact cue reactivity.
4. Subjects who are unwilling or unable to maintain abstinence from alcohol and other drugs of abuse (except nicotine) prior to and between the initial three cue procedures.
5. Subjects meeting DSM-IV criteria for substance dependence (other than nicotine, cocaine, or alcohol as appropriate) within the past 60 days.
6. Subjects currently taking B-blockers, anti-arrhythmic agents, psychostimulants or any other agents known to interfere with heart rate and skin conductance monitoring.
7. Known or suspected hypersensitivity to DCS.
8. Individuals taking medications that could adversely interact with study medications, including, but not limited to ethionamide, isoniazid, or amino acid supplements.
9. Subjects with a history of epilepsy or seizure disorder.
10. Subjects with significant liver impairment, as DCS may increase serum transaminases.