Nicotine (cont.)

Long-term use of nicotine frequently leads to addiction. Research is just beginning to document all of the changes in the brain that accompany nicotine addiction. The behavioral consequences of these changes are well documented, however.

The way that nicotine is absorbed and metabolized by the body enhances its addictive potential. Each inhalation brings a rapid distribution of nicotine to the brain -- peaking within 10 seconds and then disappearing quickly, along with the associated pleasurable feelings. Over the course of the day, tolerance develops -- meaning that higher (or more frequent) doses are required to produce the same initial effects. Some of this tolerance is lost overnight, and people who smoke often report that the first cigarette of the day is the strongest or the "best."

When a person quits smoking, they usually experience withdrawal symptoms, which often drive them back to tobacco use. Nicotine withdrawal symptoms include irritability, cognitive and attentional deficits, sleep disturbances, increased appetite, and craving. Craving -- an intense urge for nicotine that can persist for 6 months or longer -- is an important but poorly understood component of the nicotine withdrawal syndrome. Some people describe it as a major stumbling block to quitting.

Withdrawal symptoms usually peak within the first few days and may subside within a few weeks. The withdrawal syndrome is related to the pharmacological effects of nicotine, but many behavioral factors also affect the severity and persistence of withdrawal symptoms. For example, the cues associated with smoking -- the end of a meal, the sight or smell of a cigarette, the ritual of obtaining, handling, lighting, and smoking the cigarette, the people you hung out with when you smoked, and alcohol use -- all can be powerful triggers of craving that can last or re-emerge months or even years after smoking has ceased. While nicotine gum and patches may stop the pharmacological aspects of withdrawal, cravings often persist.

Source: MedicineNet.com
http://www.medicinenet.com/nicotine/article.htm