Subjects will then receive a 12-week supply of varenicline (Champix). The study nurse will hand it to them. They will be instructed to take 0.5 mg on days 1-3, 0.5 mg twice a day (once in the morning and once in the evening, at about the same time each day) on days 4-7, and 1 mg twice a day until the end of their supply (the end of week 12).