While I was training to become a family doctor, I learned the conventional wisdom about nicotine addiction. Physicians have long believed that people smoke primarily for pleasure and become psychologically dependent on that pleasure. Tolerance to the effects of nicotine prompts more frequent smoking; when the habit reaches a critical frequency—about five cigarettes per day—and nicotine is constantly present in the blood, physical dependence may begin, usually after thousands of cigarettes and years of smoking. Within hours of the last cigarette, the addicted smoker experiences the symptoms of nicotine withdrawal: restlessness, irritability, inability to concentrate, and so on. According to this understanding, those who smoke fewer than five cigarettes per day are not addicted.

I was armed with this knowledge when I encountered the proverbial patient who had not read the textbook. During a routine physical, an adolescent girl told me she was unable to quit smoking despite having started only two months before.

I thought this patient must be an outlier, a rare exception to the rule that addiction takes years to develop. But my curiosity was piqued, so I went to the local high school to interview students about their smoking. There a 14-year-old girl told me that she had made two serious attempts to quit, failing both times. This was eye-opening because she had smoked only a few cigarettes a week for two months. When she described her withdrawal symptoms, her story sounded like the lament of one of my two-pack-a-day patients. The rapid onset of these symptoms in the absence of daily smoking contradicted most of what I thought I knew about nicotine addiction. And when I tracked that received wisdom back to its source,
I found that everything I had learned was just a poor educated guess.

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