. Cigarette smoking. 65-year-old man lighting a cigarette with a lighter. Tobacco contains a range of harmful chemicals, including nicotine. It takes 20 seconds for nicotine to reach the brain and it is considered by some to be as addictive as heroin and cocaine. Tabacco contains tar, one of many carcinogens found in tobacco. It produces the chronic irritation of the respiratory system that can lead to lung cancer. Tabacco smoking is also associated with chronic bronchitis and coronary heart disease. MODEL RELEASED