Minnesota Nicotine Withdrawal Scale (MNWS): Nicotine withdrawal could have a significant impact on our study outcomes. The MNWS is a 15-item self-report scale of behaviors associated with nicotine withdrawal. Subjects answer each question using a 5-point Likert scale ranging from (0) none to 4 (severe). Smokers will be asked to fill-out the questionnaire both before (prior to medication administration) and after the scanning sessions. Group differences in the severity of nicotine withdrawal may be used as covariates in the analysis.