Nicotine dependence may be inborn.

Why do some people become heavy smokers while others smoke occasionally and others avoid tobacco altogether? The question long has puzzled researchers studying patterns of nicotine use. Ovide Pomerleau, director of the Behavioral Medicine Program, University of Michigan Department of Psychiatry, suggests that vulnerability to nicotine dependence may be an inherited trait.

The traditional explanation of how an individual becomes dependent on nicotine is that it is a matter of exposure. "The theory has been that if a person receives enough social reinforcement to overcome the initial adverse effects of smoking, [he or she] will ultimately become less sensitive to nicotine and begin to smoke regularly. This new model suggests that if a person reacts very strongly when first exposed to nicotine, perhaps gagging, but also experiencing some pleasurable effects, he or she is more likely to develop a tolerance for the drug and require it in larger doses. Therefore, the heaviest smokers seem to be the people who started out highly sensitive to nicotine."

A device that administers precise doses of nicotine in aerosol form allowed measurements of subjective, physiological, and biochemical reactions to the drug in smokers and nonsmokers. and highlighted the individual differences in the way people react to nicotine. "We found that nonsmokers required only about one-third the dose of nicotine as heavy smokers to achieve comparable plasma concentrations, indicating that heavy smokers are able to develop a metabolic tolerance for nicotine and distribute the drug more efficiently." That relationship appears to reverse itself after deprivation. Changes in heart rate and blood pressure were most pronounced in heavy smokers exposed to nicotine after a short period of...