The mishmash of physiological and psychological effects provides many positive reinforcements that smoking quickly becomes an established habit. As the term tolerance implies, a smoker actually becomes accustomed to having a certain level of nicotine in his or her body. In fact, research studies have shown that (without realizing it) smokers regulate the number of cigarettes they smoke in order to maintain their own personally preferred level of nicotine. For example, smokers who are given a very high nicotine cigarette will puff less often than usual, so they dont take in more nicotine than their preferred amount. Likewise, with a low nicotine cigarette, the smoker will take more puffs than usual, in order to get that preferred amount of nicotine.

To ease these withdrawal effects of nicotine after quitting smoking, many smokers must continue to take in their usual amount of nicotine. This is a sign of physical dependence on nicotine. Doctors define physical dependence as a change in the bodys functioning that is produced by repeated administration of a drug, such that continued doses of the drug are needed to prevent withdrawal symptoms.

But thats not all. Smokers also become accustomed to the psychological effects of smoking. After the smoking habit is established, the smoker needs to smoke in to feel normal. In other words, the effects produced by nicotine, and the behaviors associated with smoking, become necessary to maintain the persons optimal state of well-being. This condition is referred to as psychological dependence.