This double-blind, randomized assignment study will consist of three distinct phases (placebo, bupropion, and memantine). Each phase will include 10 days of outpatient medication maintenance, followed by 3 days of inpatient testing. During the outpatient phase, study visits will occur every 2 to 3 days. At these visits, compliance and side effects of medication will be monitored, smoking diaries will be collected, and medication will be dispensed. During the inpatient period participants will be allowed to smoke only at designated times. A variety of assessment will be conducted, including abstinence symptoms, acute effects of cigarettes, responses to cigarette cues, and cigarette self-administration.