This study will assess the effect of acute treatment with varenicline and placebo on early tobacco withdrawal, acute effects of cigarettes and cigarette self-administration in cigarette-smoking volunteers. After overnight abstinence, participants will come into the lab and receive acute treatment with varying doses of varenicline or placebo and perform computer tests and fill out questionnaires. Then they will be given the opportunity to smoke under operational conditions (cigarette versus money choice). This study will employ a within-group, double-blind, randomized and counterbalanced design.