Tobacco use is a form of drug addiction, as shown by studies assessing the abuse liability of tobacco and nicotine in humans and animals. Tobacco experimentation frequently leads to daily use, which is characterized by a highly consistent pattern of drug intake. Such a pattern is controlled by the biologic concentrations of nicotine, a psychoactive constituent of tobacco smoke. Nicotine is a euphoriant, self-administered by humans as well as by animals in laboratory settings. Nicotine controls smokers' behavior in such a way that reducing or suppressing tobacco consumption produces a withdrawal syndrome characterized by irritability, difficulty concentrating, cognitive impairments, and weight gain. Nonpharmacologic factors are also important determinants of tobacco addiction that interfere with successful cessation. Strategies to treat tobacco addiction are comparable to those developed for other drug addictions. For example, therapy may include the use of alternate forms of nicotine and possibly also nicotine antagonists and medications targeted to alleviate specific withdrawal symptoms, if such therapies become available. As in all drug addiction treatment strategies, behavioral intervention is important whether or not a medication is used.