MODEL RELEASED. Smoking. Woman breathing out the smoke from a cigarette (not seen). 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. Tobacco contains carcinogens, such as tar. It produces the chronic irritation of the respiratory system that can lead to lung cancer. Tobacco smoking is also associated with chronic bronchitis and coronary heart disease.