Tobacco use is the leading preventable cause of disease, disability, and death in the United States. Cigarette smoking results in more than 400,000 preventable deaths each year – about one in every five U.S. deaths. Despite the well-documented health costs of smoking, many smokers have great difficulty quitting, and many others are still becoming addicted – about 1200 per day in the U.S. Researchers are striving to understand the numerous effects of nicotine on the brain and body, determine why it is so addictive, and help smokers break its hold for good.