This double-blind study will consist of three phases (placebo, bupropion, and memantine). Each phase will include 10 days of outpatient medication maintenance, followed by 5 days of inpatient testing. During the outpatient phase, study visits will occur every 2 to 3 days. During the first portion of inpatient stay, participants will not be permitted to smoke. During the second portion of inpatient stay, smoking reinstatement will be modeled, as participant will have opportunity to smoke. A variety of behavioral, subjective, physiological, and performance measures will be assessed throughout the study.