Behavioral therapy paired with drug therapy might be a more effective treatment approach to marijuana dependence than behavioral therapy alone. Selegiline is a monoamine oxidase-B inhibitor. It increases dopamine activity in parts of the brain that are involved in dependence on addictive drugs such as nicotine, cocaine, and marijuana. Selegiline has been effective in treating nicotine dependence, but has not yet been studied in treating marijuana dependent individuals. The purpose of this study is to evaluate the effectiveness of selegiline in treating marijuana dependent individuals. Specifically, this study will determine whether selegiline reduces marijuana craving and withdrawal symptoms, thus leading to reduction or abstinence in marijuana use.