nicotine

nicotine, naturally occurring alkaloid produced by tobacco plants and related species. Nicotine is the primary psychoactive and addictive substance in tobacco products, including cigarettes, cigars, smokeless tobacco, and many electronic cigarettes (e-cigarettes). By acting on the nervous system, nicotine can increase alertness and attention while also producing dependence that makes quitting tobacco difficult.

Both the tobacco plant (Nicotiana tabacum) and the compound are named for Jean Nicot, a French ambassador to Portugal, who sent tobacco seeds to Paris in 1550. Crude nicotine was known by 1571, and the compound was obtained in purified form in 1828; the correct molecular formula was established in 1843, and the first laboratory synthesis was reported in 1904.

Physical characteristics

Tobacco plants synthesize nicotine in their roots and transport it to their leaves, where it serves as a natural chemical defense against insects and other herbivores. In total, it constitutes about 5 percent of the plant by weight and is one of the few liquid alkaloids. In its pure state it is a colorless, odorless liquid with an oily consistency, but when exposed to light or air, it acquires a brown color and gives off a strong odor of tobacco. Nicotine’s chemical formula is C₁₀H₁₄N₂.

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Mechanism of action

Nicotine acts by binding to nicotinic acetylcholine receptors (nAChRs) in the brain and nervous system. This stimulates the release of neurotransmitters—including dopamine, norepinephrine, acetylcholine, and serotonin—that influence attention, learning, mood, heart rate, and reward. In its psychoactive effects, nicotine exhibits a biphasic effect. It primarily acts as a stimulant, increasing alertness and heart rate. However, many users report feelings of relaxation and calm, affects attributed to the relief of withdrawal symptoms that develop between doses.

Nicotine dependence and addiction

Nicotine is among the most addictive naturally occurring substances known. Its addictive properties are triggered by its stimulation of dopamine release within the brain’s reward pathways, which reinforces repeated use. Because nicotine reaches the brain within seconds when inhaled in tobacco smoke or aerosol from e-cigarettes, the drive for repeated use develops rapidly. With continued exposure, the brain adapts by altering the number and sensitivity of nAChRs, leading to tolerance, in which progressively larger or more frequent doses are required to produce the same effects. Continued nicotine use also leads to physical dependence, in which the body adapts to the continual presence of nicotine.

Together, nicotine addiction—the compulsive need to use tobacco or other nicotine-containing products—and dependence, or the body’s need for nicotine and the withdrawal symptoms that result from its absence, form the basis of nicotine use disorder. In affected individuals, when nicotine intake is reduced or stopped, withdrawal symptoms—including cravings, irritability, anxiety, difficulty concentrating, increased appetite, and sleep disturbances—commonly develop.

Nicotine replacement therapy

Nicotine replacement therapy (NRT) is a widely used treatment for nicotine dependence. Unlike cigarettes and other combustible tobacco products, NRT delivers nicotine without the tar and other carcinogenic (cancer-causing) compounds generated during tobacco combustion. By maintaining lower, more stable nicotine concentrations in the bloodstream, NRT reduces withdrawal symptoms and cravings while helping users gradually discontinue nicotine use. Examples of NRT formulations include transdermal patches, chewing gum, lozenges, oral inhalers, and nasal sprays.

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Commercial and agricultural uses

Because nicotine is highly toxic to many insects, it was widely used as a natural insecticide beginning in the 19th century. Although its agricultural use has declined owing to concerns about toxicity and the availability of safer alternatives, nicotine served as the chemical model for the development of neonicotinoids, a class of synthetic insecticides that remains widely used in agriculture.

Historically, nicotine also served as a starting material for the laboratory synthesis of nicotinic acid (niacin, or vitamin B3). Modern industrial production of niacin, however, generally relies on other chemical processes. Today, most commercially produced nicotine is used in pharmaceutical NRTs, as well as in e-cigarette liquids and other nicotine-delivery products. Nicotine is also used extensively in biomedical and pharmacological research to investigate the function of nAChRs, addiction, and nervous system signaling.