Varenicline (trade name Chantix in the USA and Champix in Canada, Europe and other countries, marketed by Pfizer, usually in the form of varenicline tartrate), is a prescription medication used to treat smoking addiction. Varenicline stimulates nicotine receptors more weakly than nicotine does, that is, it is a nicotinic receptor partial agonist. In this respect it is similar to cytisine and different from the nicotinic antagonist, bupropion, and nicotine replacement therapies (NRTs) like nicotine patches and nicotine gum. As a partial agonist it both reduces cravings for and decreases the pleasurable effects of cigarettes and other tobacco products. Through these mechanisms it can assist some patients to quit smoking.

Varenicline is indicated for smoking cessation. It is more effective than NRTs and nicotine agonists. In a 2006 randomized controlled trial sponsored by Pfizer, after one year the rate of continuous abstinence was 10% for placebo, 15% for bupropion and 23% for varenicline. In a 2009 meta-analysis of 101 studies funded by Pfizer, varenicline was found to be more effective than bupropion (odds ratio 1.40) and NRTs (odds ratio 1.56).