Brief Summary: RATIONALE: Bupropion may help people stop smoking by decreasing the symptoms of nicotine withdrawal. Giving bupropion over a longer period of time may be effective in helping people stop smoking. PURPOSE: This randomized phase II trial is studying how well bupropion works in helping adults stop smoking.

Detailed Description: OBJECTIVES: Primary * Determine the feasibility of conducting a full-scale clinical trial to evaluate whether extending the duration of pre-cessation bupropion hydrochloride enhances smoking cessation, as measured by 3-month prolonged abstinence rates, in adult smokers. Secondary * Assess baseline smoking and mood characteristics (nicotine dependence, smoking history, anxiety, and depression). * Assess measures to address the hypothesized extinction mechanism (subjective effects of smoking, collection of cigarette butts for an assessment of nicotine and tar exposure, craving for smoking, and expectations for the consequences of smoking). * Assess changes in affective state as measured by Withdrawal Symptoms Checklist and by Positive and Negative Affect Schedule (PANAS) questionnaire. * Assess side effects, pill counts, and changes in daily smoking rate. * Assess mental health, personality traits, interpersonal skills, demand simulation, impulsivity, motivation, and perceived stress using validated measures. OUTLINE: Participants are stratified according to gender. Participants are randomized to 1 of 2 pre-cessation intervention arms. * Arm I (1-week run-in): Participants receive an oral placebo once or twice daily in weeks 1-3 followed by oral bupropion hydrochloride once or twice daily in week 4. Participants also undergo 90-minute behavioral group counseling sessions once in weeks 1, 2, and 4. * Arm II (4-week run-in): Participants receive oral bupropion hydrochloride once or twice daily in weeks 1-4. Participants also undergo 90-minute behavioral group counseling sessions once in weeks 1, 2, and 4. In both arms, participants are asked to quit smoking (target quit date) in week 5. All participants then receive oral bupropion hydrochloride once or twice daily in weeks 5-11 and undergo 90-minute behavioral group counseling sessions once in weeks 5, 7, and 9. Participants complete questionnaires to collect information on tobacco use history, health habits, depression, anxiety scales/symptoms, and sociodemographics at baseline. Participants also complete a series of validated questionnaires about smoking patterns, smoking satisfaction, mental health, personality traits, interpersonal skills, demand simulation, impulsivity, motivation, and perceived stress at baseline and then periodically during study. Participants undergo saliva sample collection at baseline and then periodically during study. Samples are analyzed for the presence of cotinine. Buccal cells are also collected at baseline for subsequent DNA analyses. Cigarette butts from the first cigarette of the day, including the quit day, are collected during group counseling sessions in weeks 1, 2, 4, and 5 and are assessed for a marker that indicates the amount of nicotine and tar consumed. After finishing study treatment, participants are followed at 6 and 12 months.