How long does it take to become addicted to tobacco?
Historically, researchers believed that it took about two years of regular use before one became tobacco dependent. Regular use has been ill defined, but was generally thought of as daily smoking of even a few cigarettes. More recently, Dr. Joseph DiFranza of the University of Massachusetts published an article in September of2007 in the journal of Tobacco Control in which he argued that the beginning symptoms of addiction can take hold in teenagers as rapidly as after one cigarette. Dr. DiFranza wrote a summary article about his findings in the May 2008 edition of Scientific American postulating a new theory of nicotine dependency based upon some startling facts he and several colleagues discovered (Appendix). They found that many teens reported becoming addicted to cigarettes rapidly, smoking as little as only a few cigarettes a week for two months. Even smokers who were not daily users experienced withdrawal symptoms. In fact, an average of only two cigarettes a week could precipitate withdrawal symptoms, making it difficult for them to stop. Researchers working with laboratory rats found that the nicotine from one cigarette occupied close to 90% of the receptors in the brain and that after only two consecutive days of exposure, up-regulation of nicotine receptors occurred. Dr. DiFranza speculates that regular tobacco use, whether it is monthly, weekly, or daily, is not because the user finds pleasure in it but really because the user is attempting to suppress withdrawal, however mild and unconscious that sensation may be.
DiFranza terms his theory the Sensitization-Homeostasis Theory. He believes that the direct immediate action of nicotine is purely to suppress craving due to the increased sensitization that occurs even after the first dose, which only increases with further doses. That is the sensitization part of the theory. The homeostasis part of the theory comes in when the next dose of nicotine quickly suppresses craving and restores the newly adapted homeostatic system. Thus, there are two competing systems that are generally in a natural balance: the craving-inhibition system and the craving-generation system. When one system is activated, the other responds in order to counter the activation. Nicotine activates the craving- inhibition system. The brain then attempts to restore this balance by activating the craving-generation system, prompting one to smoke again and, like a see-saw effect, these two systems are forever out of balance. The craving-generation system is usually activated via various sensory cues such as taste, sight, and smell.
Support for this theory comes from two sources. First, functional magnetic resonance imaging (fMRI) studies have demonstrated that various cues associated with using tobacco in smokers cause areas of their brains to light up, which are then suppressed after the person smokes. Secondly, people who relapse after three months of quitting resume smoking at about 40% of their previous levels. This number does not change regardless of whether the person resumes smoking at three months or even three years, suggesting that there is a permanent change in the brain impacting the craving- generation system.
However, former smokers don't crave cigarettes indefinitely. Eventually their craving goes away. New adaptations in the brain occur from abstinence, which work to inhibit the craving- generation system in order to restore the balance and return to homeostasis. These adaptations are unlike smokers or non- smokers and have been visualized experimentally in laboratory animals before, during, and after exposure to nicotine.
-  A theory of addiction involving two complementary systems, the craving- generation system and the craving- inhibition system, which helps to explain how a person can become addicted to tobacco after only a few cigarettes.
-  A type of noninvasive imaging study that allows the observer to visualize the areas of the brain that are functioning after exposure to a particular brain activity.