Tobacco use is the leading preventable cause of death in the United States. Recent research on the effects of nicotine on the brain and behavior presents an opportunity to advance medication development. Neurotransmission at NMDA receptors in the brain is associated with learning and memory and has been linked to many of nicotine's effects on humans. It is possible that altering NMDA neurotransmission may be helpful in treating nicotine addiction. The goal of this study is to evaluate the effects of memantine, an NMDA receptor antagonist, using the laboratory model of smoking relapse in nicotine dependent volunteers. The effects of memantine used in combination with bupropion, a medication currently used to facilitate smoking cessation, will be compared to a placebo.