Why People Smoke?

Smoking is a complex behavior that is initiated and maintained for different reasons. External factors such as the influence of peers, parents, and the media appear to be most important in the initiation of smoking. Adolescents whose parents and friends smoke are more likely to begin smoking. Once the smoking habit is established, it is sustained by both biologic and psychosocial factors.

Nicotine is the constituent of tobacco smoke that is responsible for causing physiological dependence on cigarettes. Chronic nicotine exposure produces changes in the brain, such as the upregulation of nicotinic acetylcholine receptors, which lead to tolerance and a craving for cigarettes when smoking stops. Smokers smoke to maintain a constant level of nicotine to avert the nicotine withdrawal syndrome, symptoms of which include restlessness, irritability, impatience, difficulty concentrating, an anxious or depressed mood, and an increased appetite. Nicotine withdrawal symptoms begin within a few hours of smoking cessation, peak 48 to 72 hours later, and gradually wane over weeks. The duration and the severity of nicotine withdrawal are highly variable, representing different degrees of nicotine addiction among smokers. No biochemical test can measure nicotine addiction, but heavily addicted smokers tend to have their first cigarette shortly after arising (i.e., within 30 minutes), smoke more cigarettes per day, and have difficulty when forced to abstain from cigarettes for even a few hours. This model of pharmacologic dependence can explain the initial difficulties that smokers have when they stop smoking but cannot alone explain why smokers have difficulty remaining abstinent after the first few weeks.

Cigarette smoking is also a habit, a learned behavior that continues because it is rewarding to the smoker. Certain repeated situations, such as finishing a meal, become strongly associated with smoking and trigger the urge to smoke. Cravings for cigarettes, which are produced by a combination of learned associations and physical changes in the brain, last longer than nicotine withdrawal symptoms and can trigger both early and late relapses in smokers who stop smoking. Smokers also use cigarettes to handle environmental stress and regulate emotions, especially strong negative emotions like anger or frustration. There is a strong epidemiologic association between depression and smoking. Smokers are much more likely than nonsmokers to have a current or past history of depression. Nicotine withdrawal symptoms are more intense in smokers with comorbid depression or depressive symptoms, and stopping smoking can trigger or worsen depressive symptoms in smokers with a depression history. This may explain the observation that smokers with depression are less likely to succeed at quitting.