Dopamine, a type of neurotransmitter, is the brain's "feel good" chemical. The amount of dopamine in the body may be an important factor in how cocaine addicts respond to treatment. Disulfiram, like cocaine, enhances dopamine activity. Upon taking disulfiram, subsequent intake of cocaine may elevate dopamine to excessive levels that produce extreme discomfort. DBH is an enzyme that breaks down dopamine. A particular variation in the DBH gene can affect the amount of dopamine that is released in the body. Therefore, cocaine addicts with varying DBH genes may respond differently to treatment. The purpose of this study is to compare the effectiveness of disulfiram in preventing relapse among methadone-maintained individuals addicted to both cocaine and opioids who may have different DBH genes.