is a potent alkaloid found in several flowering plants and is a stimulant drug. This drug is addictive. In lesser doses (an average cigarette yields about 2 mg of absorbed drug), the substance acts as a stimulant in mammals, while high amounts (50–100 mg) can be harmful. This stimulant effect is a contributing factor to the addictive properties of tobacco smoking. Nicotine’s addictive nature includes psychoactive effects, drug-reinforced behavior, compulsive use, relapse after abstinence, physical dependence and tolerance.
When a cigarette is smoked, nicotine-rich blood passes from the lungs to the brain within seven seconds and immediately stimulates nicotinic acetylcholine receptors; this indirectly promotes the release of many chemical messengers such as acetylcholine, norepinephrine, epinephrine, arginine vasopressin, serotonin, dopamine, and beta-endorphin in parts of the brain.