Randomization was performed using the Pocok-Simon approach, which is a dynamic allocation procedure that balanced the marginal distributions of the stratification factors between treatment groups (Pocock and Simon 1975). Stratification factors were: site, gender, number of cigarettes smoked per day (10–39 vs. 40 or more), and number of years smoked (<5, 5–9, >9). Randomization assigned subjects to one of three medications.
