Nearly 80% of the smokers who try to quit relapse within six months, and nicotine is the main reason why. A new brain imaging study supported in part by NIH’s National Institute on Drug Abuse (NIDA) shows how the nicotine in just a few puffs of a cigarette can drive someone to continue smoking.

Dr. Arthur Brody of the David Geffen School of Medicine at UCLA and his colleagues used positron emission tomography (PET) to scan the brains of 11 smokers and assess nicotine’s activity. They used a recently-developed radiotracer that binds nicotine receptors but can be displaced when nicotine comes in to bind the receptors instead. During scanning, the participants smoked different amounts. Their craving was measured with the Urge to Smoke scale, which assesses responses to 10 craving-related questions.

In the August 2006 issue of the Archives of General Psychiatry, the researchers report that the amount of nicotine in just one puff of a cigarette occupied about 30% of the brain’s most common type of nicotine receptors, while three puffs of a cigarette occupied about 70%. Smoking a whole cigarette filled more than 88% of the receptors and alleviated craving to some extent. Only when nearly all of the receptors were occupied, however, after smoking at least 2 and a half cigarettes, did the smokers becomes satiated, or satisfied, for a time. Soon, however, this level of satiation wore off, driving the smoker to continue smoking throughout the day to satisfy their cigarette cravings.

“The central findings of the study suggest that typical daily smokers need to have these nicotine receptors almost completely saturated throughout the day, which drives the almost uncontrollable urge to keep smoking,” says Dr. Nora D. Volkow, Director of NIDA. “A more complete understanding of how nicotine affects the brain can help us develop better therapies for people looking to quit.”