We collected baseline questionnaire data on age, race, sex, marital status, presence of other smokers in the household, level of education, history of drug or alcohol abuse, medical illness, and history of depression. Body mass index (calculated as weight in kilograms divided by the square of height in meters) and change in weight over time were determined using self-reported or medical record data. Medical problems, such as coronary disease, chronic obstructive pulmonary disease, vascular disease, diabetes mellitus, hypertension, and tobacco-related malignancy (ie, cancer of the lung, bladder, kidney, oropharynx, and larynx) were recorded based on participant interviews and, when available, medical chart review. We obtained self-reported data on preenrollment level of cigarette smoking (in cigarettes per day), pack-years of tobacco smoked (average packs per day multiplied by the number of years of smoking), and number of prior attempts at smoking cessation. Estimated level of nicotine dependence was based on the Fagerström Tolerance Questionnaire.15 Two 20-item self-efficacy questionnaires were administered at baseline to assess whether confidence in quitting and resistance to the temptations of smoking were associated with long-term cessation.16 Symptoms of nicotine withdrawal were assessed at 1 week, 8 weeks, and 12 weeks after self-reported quitting using a previously described withdrawal scale.7 The 9 items included in the withdrawal scale included craving for a cigarette, depressed mood, difficulty falling asleep, awakening at night, irritability/frustration/anger, anxiety, difficulty with concentration, restlessness, and increased appetite. Each symptom was scored from 0 (absent) to 4 (severe), and the scores for each of the 9 items were summed for each participant who reported quitting.