Nicotine

Nicotine is an alkaloid—a nitrogen-containing organic compound derived from plants—obtained from the tobacco plant (Nicotiana). It is a principal addictive substance in cigarettes and tobacco products.

When inhaled as smoke or absorbed through other routes, nicotine reaches the brain within seconds. There it binds to receptors called nicotinic acetylcholine receptors, triggering the release of dopamine and other neurotransmitters that affect mood, alertness, and reward-related behaviour.

Origin and chemical properties

The plant produces nicotine as a natural defense against insects; it acts as a neurotoxin to insect nervous systems. Tobacco leaves contain the highest concentrations. Nicotine is a colourless oily liquid in its pure form, but turns brown when exposed to air.

Addiction

Nicotine is one of the most addictive substances known. Repeated use causes changes in the brain; cessation can trigger withdrawal symptoms including anxiety, irritability, insomnia, and intense cravings. For this reason, most people find quitting difficult.

Routes of administration

Beyond cigarettes, nicotine is obtained through chewing tobacco or snuff, and electronic cigarettes (e-cigarettes), which deliver nicotine vapour by heating a liquid. There are also medicinal products designed to aid cessation—such as patches, gum, and inhalers—that deliver nicotine to the body without smoke inhalation.