This study is designed to examine the behavioral responses a cigarette smoker may have to using varenicline. Behavioral responses may help to better understand its mechanisms which in turn could improve treatment outcomes. The primary hypothesis for the study is to observe decreases in smoking topography, an objective measure of smoking behavior or puffing, on varenicline, relative to placebo; and decreases on day 21 relative to day 7 during varenicline treatment. We will also examine puffing and nicotine cigarette choices during lab visits at baseline, and Days 7 and 21. We also propose to examine if extended duration of treatment has clinical significance in decreasing smoking behaviors, thus potentially increasing the efficacy of varenicline.