Nicotine is the main addictive chemical in tobacco products, such as cigarettes and cigars. Nicotine occurs naturally, other chemicals such as ammonia, menthol, etc. are the additives. Nicotine acts in the brain by stimulating the adrenal glands to release the hormone epinephrine (adrenaline) and by increasing level of messenger dopamine. Cigarette smoking can lead to lung cancer, chronic bronchitis, and emphysema. It increases the risk of heart disease, which can lead to stroke or heart attack. Brain changes brought by continued nicotine exposure result in addiction.

Nicotine is a chiral alkaloid (cyclic organic compounds that contain nitrogen in a negative oxidation state) that is naturally produced in the nightshade family of plants (most predominantly in tobacco) and is widely used recreationally as a stimulant. As a pharmaceutical drug, it is used for smoking cessation to relieve withdrawal symptoms. Nicotine is highly addictive unless used in slow-release forms. Nicotine addiction involves drug-reinforced behavior, compulsive use, and relapse following absistence.

An average cigarette yields about 2 mg of absorbed nicotine. The estimated lower dose limit for fatal outcomes is 500-1000 mg of ingested nicotine for an adult (6.5-13 mg/kg).

More Info: teens.drugabuse.gov