The carbon monoxide from smoking is the same as gas from car exhausts. It leaves the heart with less oxygen, making it harder for heart and brain to work. Nicotine is an addictive poison used in insecticides, it affects blood vessels, raises blood pressure and increases heart rate. Tars are poisonous chemical compounds which collect in the lungs and can cause cancer. In fact tobacco smoke contains over 4,000 chemicals at least 43 of which are known to cause cancer.
Nicotine produces different effects on the body simultaneously.
It stimulates the system as it makes you feel relaxed. New smokers often feel dizzy and sick from tobacco smoke. As they continue to smoke, their bodies learn to depend on nicotine and they smoke more and more. Smoking is often tied to certain moods, events or places. Smoking doesn't just harm a smoker's lungs, it rots them.