The main ingredients of a cigarette are nicotine, tar, carbon monoxide and more than 4000 chemicals. Burning a cigarette produces smoke that contains tar particles. Nicotine, once absorbed, is quickly transported by the blood to the brain within 7 seconds, stimulating certain brain cells to develop nicotine-sensitive receptors. When these receptors bind with nicotine, the release of dopamine in the brain increases, and pleasant, relaxing sensations are produced. The drop in nicotine intake will lower the dopamine level in the brain, producing different kinds of discomfort symptoms. Since smoking reduces the unpleasant symptoms, one gradually becomes dependent on cigarette smoking to release the withdrawal symptoms. Repetitive smoking of cigarettes eventually leads to addiction.
During smoking cessation, the nicotine-sensitive receptors in the brain decrease in number as a result of prolonged deprivation of nicotine, and the normal secretion of dopamine is no longer interfered with. However, when an ex-smoker is exposed to nicotine again, the nicotine receptors in the brain return to the previous state in a very short period of time. To maintain the stability of dopamine levels, nicotine intake is required and addiction is very likely to occur again.
