Overview: Its expensive, offensive, addictive, and practically guaranteed to ruin your health. Still, despite mounting evidence of its health hazards, massive judgments against the tobacco industry for product liability, and major tax increases, smoking is still very much with us. It's still such a part of so many lives, in fact, that the World Health Organization estimates that it kills someone, somewhere, every 10 seconds.

Appearance: Cigarettes are made from the shredded leaves of the tobacco plant. Shredded tobacco is also used in pipe smoking mixtures, while cigars are rolled from whole-leaf tobacco.

Actions/Effects: The drug nicotine is a stimulant which is released from tobacco as it burns and is inhaled into the body. A typical cigarette contains 10-20 mg of nicotine, but less than 1 mg reaches the smoker's lungs. Nicotine is absorbed into the bloodstream by structures in the lungs called alveoli. In the central nervous system, nicotine acts on receptors for the neurotransmitter acetylcholine, raising heart rate and blood pressure. Subjective effects include feelings of relaxation, increased alertness, and decreased appetite.

Risks/Side Effects: Common problems include coughing, shortness of breath, and increased susceptibility to colds. Risks increase over time, and include a higher risk of pneumonia, bronchitis, and oral and throat cancers. Long-term smoking can cause heart disease, stroke, emphysema, and lung cancer. Smoking during pregnancy is linked with a number of problems, especially lower birthweight. In addition, smoking by the mother -- both during pregnancy and after delivery -- increases the risk of Sudden Infant Death Syndrome.

Addiction Potential: Nicotine is highly addictive -- so much so that 70 percent of smokers who quit ultimately relapse during the first year, according to a recent report by the American Psychiatric Association.

Trends: Measures to restrict smoking and to discourage teens from starting seem to be paying off. Smoking rates are down among virtually all U.S. demographic groups, and teen smoking, which surged briefly during the mid-1990's, has fallen sharply in recent surveys.

Demographics: Today, 44.5 million American adults smoke -- 20.9 percent of the adult population, down from 43 percent in the mid-'60s. Teen smoking is also down: The number of high school seniors who admitted lighting up in the previous month totalled 21.6 percent in 2006, down from 36.5 percent in 1997.