Nicotine, one of more than 4,000 chemicals found in the smoke from tobacco products such as cigarettes, cigars, and pipes, is the primary component in tobacco that acts on the brain. Smokeless tobacco products such as snuff and chewing tobacco also contain many toxins as well as high levels of nicotine. Nicotine, recognized as one of the most frequently used addictive drugs, is a naturally occurring colorless liquid that turns brown when burned and acquires the odor of tobacco when exposed to air. Since nicotine was first identified in the early 1800s, it has been studied extensively and shown to have a number of complex and sometimes unpredictable effects on the brain and the body.
Cigarette smoking is the most prevalent form of nicotine addiction in the United States.
Through inhaling smoke, the average smoker takes in 1 to 2 mg nicotine per cigarette. There have been substantial increases in the sale and consumption of smokeless tobacco products also, and more recently, in cigar sales. Nicotine is absorbed through the skin and mucosal lining of the mouth and nose or by inhalation in the lungs. Depending on how tobacco is taken, nicotine can reach peak levels in the bloodstream and brain rapidly. Cigarette smoking, for example, results in rapid distribution of nicotine throughout the body, reaching the brain within 10 seconds of inhalation.