Are there other chemicals that may contribute to tobacco addiction?
Yes, research is showing that nicotine may not be the only psychoactive ingredient in tobacco. Using advanced neuroimaging technology, scientists can see the dramatic effect of cigarette smoking on the brain and are finding a marked decrease in the levels of monoamine oxidase (MAO), an important enzyme that is responsible for the breakdown of dopamine13. This change is likely caused by some tobacco smoke ingredient other than nicotine, since we know that nicotine itself does not dramatically alter MAO levels. The decrease in two forms of MAO (A and B) results in higher dopamine levels and may be another reason that smokers continue to smoke—to sustain the high dopamine levels that lead to the desire for repeated drug use.
Recently, NIDA-funded researchers have shown in animals that acetaldehyde, another chemical constituent of tobacco smoke, dramatically increases the reinforcing properties of nicotine and may also contribute to tobacco addiction14. The investigators further report that this effect is age-related, with adolescent animals displaying far more sensitivity to this reinforcing effect14, suggesting that the brains of adolescents may be more vulnerable to tobacco addiction.
What are the medical consequences of tobacco use?
Cigarette smoking kills an estimated 440,000 U.S. citizens each year—more than alcohol, cocaine, heroin, homicide, suicide, car accidents, fire, and AIDS combined15. Since 1964, more than 12 million Americans have died prematurely from smoking, and another 25 million U.S. smokers alive today will most likely die of a smoking-related illness7.
Cigarette smoking harms every organ in the body. It has been conclusively linked to leukemia, cataracts, and pneumonia, and accounts for about one-third of all cancer deaths14. The overall rates of death from cancer are twice as high among smokers as nonsmokers, with heavy smokers having rates that are four times greater than those of nonsmokers17. Foremost among the cancers caused by tobacco use is lung cancer—cigarette smoking has been linked to about 90 percent of all lung cancer cases, the number-one cancer killer of both men and women18. Smoking is also associated with cancers of the mouth, pharynx, larynx, esophagus, stomach, pancreas, cervix, kidney, ureter, and bladder7.
In addition to cancer, smoking causes lung diseases such as chronic bronchitis and emphysema, and it has been found to exacerbate asthma symptoms in adults and children. More than 90 percent of all deaths from chronic obstructive pulmonary diseases are attributable to cigarette smoking. It has also been well documented that smoking substantially increases the risk of heart disease, including stroke, heart attack, vascular disease, and aneurysm7. It is estimated that smoking accounts for approximately 21 percent of deaths from coronary heart disease each year16.
Exposure to high doses of nicotine, such as those found in some insecticide sprays, can be extremely toxic as well, causing vomiting, tremors, convulsions, and death19. In fact, one drop of pure nicotine can kill a person. Nicotine poisoning has been reported from accidental ingestion of insecticides by adults and ingestion of tobacco products by children and pets. Death usually results in a few minutes from respiratory failure caused by paralysis.
While we often think of medical consequences that result from direct use of tobacco products, passive or secondary smoke also increases the risk for many diseases. Environmental tobacco smoke is a major source of indoor air contaminants; secondhand smoke is estimated to cause approximately 3,000 lung cancer deaths per year among nonsmokers and contributes to more than 35,000 deaths related to cardiovascular disease7. Exposure to tobacco smoke in the home is also a risk factor for new cases and increased severity of childhood asthma and has been associated with sudden infant death syndrome. Additionally, dropped cigarettes are the leading cause of residential fire fatalities, leading to more than 1,000 deaths each year20.
Are there safe tobacco products?
The adverse health effects of tobacco use are well known, yet many people do not want to quit or have difficulty quitting. As a result, there has been a recent surge in the development of tobacco products that claim to reduce exposure to harmful tobacco constituents or to have fewer health risks than conventional products. These “potentially reduced exposure products” (or PREPs), which include cigarettes and smokeless tobacco (e.g., snuff, tobacco lozenges), have not yet been evaluated sufficiently to determine whether they are indeed associated with reduced risk of disease21. Recent studies indicate that the levels of carcinogens in these PREPs range from relatively low to comparable to conventional tobacco products22,23. These studies conclude that medicinal nicotine (found in the nicotine patch and gum) is a safer alternative than these modified tobacco products.
Smoking and pregnancy—What are the risks?
In the United States, it is estimated that 18 percent of pregnant women smoke during their pregnancies1. Carbon monoxide and nicotine from tobacco smoke may interfere with the oxygen supply to the fetus. Nicotine also readily crosses the placenta, with concentrations in the fetus reaching as much as 15 percent higher than maternal levels24. Nicotine concentrates in fetal blood, amniotic fluid, and breast milk. Combined, these factors can have severe consequences for the fetuses and infants of smoking mothers. Smoking during pregnancy caused an estimated 910 infant deaths annually from 1997 through 200115, and neonatal care costs related to smoking are estimated to be more than $350 million per year7,25.
The adverse effects of smoking during pregnancy can include fetal growth retardation and decreased birth weights. The decreased birth weights seen in infants of mothers who smoke reflect a dose–dependent relationship—the more the woman smokes during pregnancy, the greater the reduction of infant birth weight26,27. These newborns also display signs of stress and drug withdrawal consistent with what has been reported in infants exposed to other drugs28. In some cases, smoking during pregnancy may be associated with spontaneous abortions, sudden infant death syndrome, as well as learning and behavioral problems in children. In addition, smoking more than a pack a day during pregnancy nearly doubles the risk that the affected child will become addicted to tobacco if that child starts smoking29.
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