Nicotine is a highly addictive substance that occurs naturally in tobacco. It is the active ingredient in tobacco smoke. It has a pungent odor and an acrid taste. Nicotine is defined as a poisonous, oily, pale yellow substance that turns brown upon exposure to air. In concentrated form, nicotine is used as a potent insecticide.

The amount of nicotine which occurs in tobacco leaves ranges from 2% to 7%.

Nicotine mimics the affects of acetylcholine (nerve signal transmitter) and it acts primarily on the autonomic nervous system. As such, it can be dangerous. Nicotine can cause respiratory failure and paralysis at doses of less than 50 mg. Smaller amounts can cause nausea, dizziness, lowered blood pressure, and heart palpitations.

A smoker inhales approximately 3mg of nicotine per cigarette. Even this small amount constricts blood vessels, increases the heart rate, and acts on the central nervous system. It also confers a feeling of well-being and alertness on the smoker.

Nicotine itself is not considered carcinogenic. However, it is likely that it contributes to the increased incidence of heart disease in smokers. It may also enhance the growth of tumors caused by carcinogens.

People who use tobacco products in any form will develop a physiological addiction to nicotine. Proven to increase the flow of dopamine, a neurotransmitter, nicotine creates pleasurable feelings in the user, along with a desire to maintain them. When nicotine levels in the blood drop, smokers will develop withdrawal symptoms within 48 to 72 hours after the last cigarette. Withdrawal symptoms include anxiety, difficulty sleeping, irritability, heart rate and blood pressure changes, changes in brain waves, and sleeping problems.

The symptoms are so unpleasant that most smokers will resume smoking in an effort to raise nicotine levels in the blood to the point where the symptoms subside.

Many people try nicotine-containing chewing gums and adhesive skin patches in an effort to quit smoking. The rate of nicotine absorption is slower in these methods than it is with smoking and it does not provide the same pleasurable sensations; gums and patches, however, can help alleviate withdrawal symptoms.

It is important not to mix gums or patches with cigarettes, as this can lead to toxicity and nicotine overdose, which causes headache, palpitations, and nausea.

Other nicotine-delivery methods include nasal sprays and inhalers which more closely mimic the delivery and impact of nicotine as obtained by smoking.

Prolonged use of nicotine replacements, especially inhalers, is not recommended for more than a few months. Research has shown that extended use of these products could damage the cells lining the lungs and blood vessels.