Cigarette smoking becomes the single most preventable cause of death in the world, according to a lot of studies. Tobacco use also causes chronic lung disease (emphysema and chronic bronchitis), cardiovascular disease, stroke, cancer and cataracts.

But nicotine, a powerful central nervous system stimulant found naturally in the tobacco leaf, is classified as a drug. It is one of the main ingredients in tobacco and in higher doses, nicotine is extremely poisonous. It is commonly used as an insecticide.

Nicotine is considered also highly addictive. The addictive effect of nicotine is the main reason why tobacco is widely used. Many smokers continue to smoke in order to avoid the pain of withdrawal symptoms. Smokers also adjust their behavior (inhaling more deeply, for example) to keep a certain level of nicotine in the body.

Smokers who usually smoke at least 15 cigarettes per day or smoke their first cigarette of the day within 30 minutes of waking are likely to experience nicotine withdrawal symptoms. They will likely find quitting uncomfortable.

Stopping can produce unpleasant withdrawal symptoms including depression, insomnia, irritability, difficulty concentrating, restlessness, anxiety, decreased heart rate, increased appetite, weight gain, and craving for nicotine.

The risk of developing smoking-related cancers, as well as non-cancerous diseases, increases with total lifetime exposure to cigarette smoke.

Smoking cessation has major and immediate health benefits, including decreasing the risk of lung and other cancers, heart attack, stroke, and chronic lung disease.

In a study was shown that non-smokers exposed to second-hand smoke at home or work increase their risk of developing heart disease by 25 to 30% and lung cancer by 20 to 30%. And also second-hand smoke contains more than 50 cancer-causing chemicals, and is itself a known human carcinogen.

Even brief exposure to second-hand smoke has immediate adverse effects on the cardiovascular system and increases risk for heart disease and lung cancer, the report said.