Nicotine is a natural constiutent of leaves from the tobacco plant Nicotiana tabacum and is consumed primarily in the form of cigarettes, cigars, pipe tobacco and chewing tobacco. Acutely, it is a mild stimulant. With chronic use, tolerance and physical dependence develop.

• History of Nicotine
• Behavioral Effects in Humans
• Mechanism of Action
• Thought Questions and Quick Quiz
• Additional Sources of Information

The use of tobacco began with the native people of North and South America. Early Europeans visiting the New World observed Native Americans smoking cigars and chewing tobacco. When introduced by the Spanish to Europe in the early 1500s, tobacco was thought to hold medicinal properties. For example, smoke was blown into all openings of the head to treat diseases of the ear, eyes, nose, and mouth. In fact, the tobacco plant was named Nicotiana tabacum in honor of Jean Nicot, who promoted it for its medicinal value. In 1828, two French scientists isolated nicotine as the active ingredient in tobacco.

Although there have been antismoking campaigns waged since the introduction of tobacco to Europe, the use of this substance continues to be very widespread. Chronic use of tobacco is causally linked to a variety of serious diseases including coronary heart disease and several types of cancer. Use of tobacco is considered to be the largest preventable cause of death in the United States.

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Nicotine, at low to moderate doses, is a central nervous system stimulant. Effects include tremors, an increase in behavioral activity, increased alertness, facilitation of memory and release of epinephrine from the adrenal glands. In addition to these central effects nicotine increases heart rate and blood pressure, inhibitis stomach secretions and stimulates bowel activity. Individuals experienced in the use of nicotine report pleasure and relaxation from this drug. In contrast, those who have never used products containing nicotine often experience nausea and vomiting and report the effects as being unpleasant.

At high doses nicotine produces convulsions and death. Low dose stimulation of the central nervous system is followed by depression at high doses, and death results from failure of respiration due to paralysis of muscles involved in breathing.

Chronic use of nicotine leads to changes in the brain and behavior. One of the first changes is tolerance, a decrease in the effects of nicotine. Tolerance occurs rapidly to some of the upleasant effects, including dizziness, nausea and vomiting. This decrease in upleasant effects may unmask the pleasurable effects of nicotine, leading to further use of the drug. The second major change seen in response to chronic ingestion of nicotine is physical dependence. Following chronic use, there are physiological changes that lead to a requirement for the drug. With the development of physical dependence, further administration of nicotine is necessary to avoid a physiological disturbance. This disturbance is known as a withdrawal (or abstinence) syndrome. The withdrawal syndrome for nicotine, although not as behaviorally overt as that for other drugs such as ethanol or opiates, is very unpleasant for chronic users. Symptoms include confusion, anxiety, irritablility, drowsiness, dizziness, headache, nausea, disturbed sleep, increased eating and weight gain, and profound craving. According to experienced users, the nicotine withdrawal syndrome is as psychologically stressful as heroin withdrawal, and the desire to avoid this syndrome contributes significantly to further use of tobacco products.

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At low to moderate doses, nicotine is a cholinergic agonist -- it acts by stimulating nicotinic acetylcholine receptors. In fact, as the name suggests, nicotinic receptors were named after it was found that they were selectively and potently activated by nicotine.

Nicotine can be absorbed through most of the body's membranes. After nicotine is absorbed it is distributed by the blood to a number of sites of pharmacological action. The effects of nicotine can be observed rapidly, as its distribution half-life is only eight minutes.

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Thought Questions

• There is currently considerable debate over whether nicotine is "addictive" or not. Given that nicotine has many of the same properties of other addictive drugs, why do you suppose the debate continues?

• The first time individuals use tobacco products, the experience is typically considered unpleasant. Why do you suppose so many continue to use the product even in the face of these unpleasant effects?

Quick Quiz

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