 Varenicline ChantixTM, Pfizer is a novel selective nicotinic receptor partial agonist with specificity for the α4β2 nicotine acetylcholine receptor that has demonstrated remarkable efficacy for increasing long-term tobacco abstinence rates in cigarette smokers. The novel mechanism of action of varenicline potentially circumvents the limitations of using nicotine replacement therapy or bupropion pharmacotherapy in ST users. The overall goal of this line of research is to develop effective pharmacologic treatments for ST users to increase long-term 6 months abstinence rates. The central hypothesis of this application is that varenicline is efficacious for the treatment of ST users. 