• To learn more about how the drugs Bupropion and Varenicline affect mood and physiological responses in different groups of people as they attempt to quit smoking. [ Time Frame: 5 Years ] [ Designated as safety issue: No ]
  

• To learn how these drugs affect responses related to changes in emotion and whether or not a person's genetic make-up makes a difference in how they respond to the medication. [ Time Frame: 5 Years ] [ Designated as safety issue: No ]
  

Inclusion Criteria:

1. Age: 18-65 years old
2. Smoking: >/= 5 cigarettes per day within the 2 months preceding the screening visit and expired CO greater than or equal to 6 ppm.
3. Able to follow verbal and written instructions in English and complete all aspects of the study
4. Have an address and home telephone number where they may be reached
5. Provide informed consent and agree to all assessments and study procedures
6. Be the only participant in their household

Exclusion Criteria:

1. Within the month immediately preceding the screening visit; use of any form of tobacco product other than cigarettes on 3 or more days within a week only if the individual refuses to refrain from non-cigarette tobacco use during the course of this study
2. Within the month immediately preceding the screening visit; use of marijuana in any form on 3 or more days within a week
3. Within the two weeks immediately preceding the screening visit, involvement on more than 3 days in any formal smoking cessation activities
4. Current visual or auditory problems that in the opinion of the investigator would interfere with the completion of study assessments
5. Treatment on a continuous basis within 2 weeks before the screening visit: any contraindicated medication for Varenicline or Bupropion.
6. Uncontrolled hypertension or other major contraindications for Bupropion or Varenicline.
7. Severe renal impairment (<30 ml/min/1.73 m2).
8. Laboratory evaluations outside normal limits and of potential clinical significance in the opinion of the investigator
9. Meet current criteria for psychiatric disorders or substance abuse as assessed by the MINI for items A, B, D, I, J, K, L, M and N.
10. Subject rated as moderate to high on suicidality as assessed by the MINI.
11. Psychiatric hospitalization within 1 year of screening date.
12. A positive urine pregnancy test during the screening period.
13. Pregnant, breast-feeding, or of childbearing potential who is not protected by a medically acceptable, effective method of birth control while enrolled in the study
14. Use of Varenicline or Bupropion within two weeks before the screening visit.
15. History of hypersensitivity or allergic reaction to Varenicline, tricyclic antidepressant, Bupropion (Wellbutrin, Zyban) or similar chemical classes or any component of these formulations.
16. Subject considered by the investigator as unsuitable candidate for receipt of an investigational drug, or unstable to be followed up throughout the entire duration of the study.