Cocaine is one of the most widely abused drugs in the United States. Memantine is a type of drug called an NMDA receptor antagonist. It works by decreasing normal excitement in the brain. NMDA receptor antagonists have shown to reduce cocaine-induced dopamine release in animal models, as well as lessen conditioned cocaine cues. The purpose of this study is to determine the effectiveness of memantine in preventing relapse to cocaine use in cocaine dependent individuals. In addition, this study will determine whether memantine produces better results than a placebo in decreasing cocaine craving, psychological symptoms, functional impairment, and discontinuation of treatment in cocaine dependent individuals.