Nicotine, perhaps the most commonly recognized ingredient of tobacco, is an addictive central nervous system stimulant. When nicotine is taken into the lungs, it is transmitted to the brain in seconds. It causes the heart to beat more rapidly, drawing in and pushing out more blood. It also makes the veins and arteries constrict, thus requiring the heart to labor harder. This results in increased blood pressure and heart rate.
Carbon monoxide is among the many toxic chemicals present in tobacco smoke.
It impedes the ability of red blood cells to carry oxygen to bodily tissues, including heart and brain tissue. The lack of oxygen causes the heart to work harder and can lead to a thickening of the walls and possible heart failure. Despite the fact that tobacco is a stimulant, addicted smokers usually feel that smoking relaxes them. This feeling of relaxation is in reality the result of their having satisfied a physical craving. Smokers are constantly experiencing the symptoms of nicotine withdrawal, and drawing smoke into their lungs relieves these symptoms by satisfying their craving for the chemical.