The smoke from combustible tobacco products contains more than 7,000 chemicals. Nicotine is the primary reinforcing component of tobacco; it drives tobacco addiction.20,21 Hundreds of compounds are added to tobacco to enhance its flavor and the absorption of nicotine.22 Cigarette smoking is the most popular method of using tobacco; however, many people also use smokeless tobacco products, such as snuff and chewing tobacco, which also contain nicotine (see "Other Tobacco Products"). E-cigarettes, which deliver nicotine in the absence of other chemicals in tobacco, have become popular in recent years (see "What are electronic cigarettes?").
The cigarette is a very efficient and highly engineered drug-delivery system. By inhaling tobacco smoke, the average smoker takes in 1–2 milligrams of nicotine per cigarette. When tobacco is smoked, nicotine rapidly reaches peak levels in the bloodstream and enters the brain. A typical smoker will take 10 puffs on a cigarette over the roughly 5 minutes that the cigarette is lit.23 Thus, a person who smokes about 1 pack (20 cigarettes) daily gets 200 "hits" of nicotine to the brain each day. Among those who do not inhale the smoke—such as cigar and pipe smokers and smokeless tobacco users—nicotine is absorbed through mucous membranes in the mouth and reaches peak blood and brain levels more slowly.
Immediately after exposure to nicotine, there is a "kick" caused in part by the drug’s stimulation of the adrenal glands and resulting discharge of epinephrine (adrenaline). The rush of adrenaline stimulates the body and causes an increase in blood pressure, respiration, and heart rate.24 Like other drugs, nicotine also activates reward pathways in the brain—circuitry that regulates reinforcement and feelings of pleasure.20,21