What is varenicline and how does it work? Varenicline (trade name Champix) is a medicine that was first licensed in the UK in December 2006. It was developed to help smokers to stop smoking. Varenicline mimics the effect of nicotine on the body. Therefore, it both reduces the urge to smoke and relieves withdrawal symptoms. The precise action of varenicline is that it interferes with the receptors in the brain that nicotine stimulates. (The nicotine in cigarettes attaches to receptors in brain cells to stimulate part of the brain - this is how nicotine has it's effect.) What varenicline does is to partly stimulate the nicotine receptors. This mimics the effects of nicotine to reduce cravings and withdrawal effects when you stop smoking. However, at the same time, it partially blocks the receptors and prevents nicotine from attaching to the receptors. This blocks or blunts the effect of nicotine in people who give in to temptation and have a cigarette