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A South American herb, Nicotiana tabacum, that has large ovate to lanceolate leaves and terminal clusters of tubular white or pink flowers. T. leaves contain 2–8% of nicotine and are the source of smoking and chewing t.. T. smoke contains nicotine, carbon monoxide (4%), nitric oxide, and numerous aromatic hydrocarbons and other substances known to be carcinogens, including benzo[a]pyrene, β-naphthylamine, and nitrosamines.Cigarette smoking is the leading preventable cause of disease and death in the U.S., being responsible for approximately 434,000 deaths (20% of all deaths) each year. Smoking 2 packages of cigarettes a day reduces life span by 8.3 years. Smoking t. in any form (cigarettes, cigars, pipe) is a strong independent risk factor for atherosclerosis, acute myocardial infarction, unstable angina, stroke, and sudden death. It is responsible for 45% of all deaths due to coronary artery disease in men under 65 and more than 50% of all strokes in both sexes before age 65. Smoking lowers HDL cholesterol and raises LDL and VLDL cholesterol, and increases the risk of intermittent claudication and aortic aneurysm. It may cause as much as a 30-fold increase in the risk of thromboembolic disease in women taking oral contraceptives. Smoking is responsible for 100,000 deaths each year due to lung cancer, and markedly increases the risk of other cancers, particularly those of the oral cavity, larynx, esophagus, kidney, bladder, uterine cervix, and pancreas. Cigarette smoking is the principal cause of chronic bronchitis and emphysema. Passive smoking (inhalation by nonsmokers of second-hand or sidestream smoke) causes 53,000 deaths annually, 37,000 of them due to coronary artery disease. Maternal smoking during pregnancy is associated with increased risk of miscarriage, stillbirth, and low birth weight. Children of smokers are at increased risk of sudden infant death syndrome and meningococcal meningitis. Use of smokeless t. (chewing t., snuff) greatly increases the risk of cancer and premalignant lesions of the oral cavity. Nicotine use is powerfully addictive, leading to habituation, tolerance, and dependency. In the U.S., 90% of smokers become habituated to t. before age 21; 3000 children begin smoking each day. The likelihood of becoming and remaining a smoker increases in inverse proportion to the number of years of education completed. Quitting smoking decreases the risk of death from all causes by 30%. Effective strategies for smoking cessation include behavior modification therapy, nicotine replacement (gum, skin patches, inhaler), hypnosis, and drug therapy (bupropion), but the relapse rate 3 months after smoking cessation is 60%.

- wild t. SYN: lobelia.

to·bac·co tə-'bak-(.)ō n, pl -cos

1) any plant of the genus Nicotiana esp an annual So. American herb (N. tabacum) cultivated for its leaves

2) the leaves of cultivated tobacco prepared for use in smoking or chewing or as snuff

3) manufactured products of tobacco also the use of tobacco as a practice

the dried leaves of the plant Nicotiana tabacum or related species, used in smoking and as snuff. Tobacco contains the stimulant but poisonous alkaloid nicotine, which enters the bloodstream during smoking. The volatile tarry material also released during smoking contains carcinogenic chemicals (see carcinogen).