Cocaine is an extremely addictive stimulant drug that directly affects the brain. It is used in several different forms and can be snorted, smoked, or injected to achieve the desired effect. Cocaine users are at risk for many health problems, both directly and indirectly related to the effects of cocaine. Disulfiram, a drug used to treat chronic alcoholism, may be effective in reducing cocaine use. This study will evaluate the effectiveness of three different doses of disulfiram in treating cocaine dependence in opioid- and cocaine-dependent individuals maintained on methadone.