The study by Killen and colleagues1 published in this issue of JAMA may lead to improved diagnosis and treatment of nicotine dependence. Their findings extend those of the Surgeon General2 and indicate that level of nicotine dependence is a determinant of the severity of withdrawal symptoms and difficulty in quitting smoking. These kinds of observations are shared with other drug dependencies.
Killen and colleagues compared a variety of measures of nicotine withdrawal symptoms and smoking cessation difficulty in light and heavy smokers in a treatment study. Whether the person smoked fewer than 16 cigarettes per day or more than 24 cigarettes per day accounted for approximately 80% of the variance in severity of withdrawal symptoms; these cutoff values were indicative of weak or strong withdrawal symptoms, respectively. Factors such as the number of years a person had smoked, the age at which he or she started, the nicotine