The main goal of this project is to improve the current laboratory model of smoking cessation and study the mechanism involved in smoking maintenance. We hypothesize that varenicline will dose-dependently: 1) decrease nicotine withdrawal symptoms, 2) decrease acute effects of cigarettes and 3) decrease self-administration of cigarettes in the laboratory paradigm. Showing the effectiveness of varenicline in the proposed laboratory model will confirm the model's predictive validity to detect clinically effective medication.