Nicotine

Principal alkaloid of tobacco, occurring throughout the plant but mostly in the leaves. It is a heterocyclic compound, containing a pyridine ring; its chemical formula is C₁₀H₁₄N.

Nicotine is the chief addictive ingredient (&see; drug addiction) in cigarettes and cigars and in snuff. It has a unique biphasic effect: Inhaled in short puffs it is a stimulant, but when inhaled slowly and deeply it can be a tranquilizer. In larger doses, nicotine is a highly toxic poison, used as an insecticide, fumigant, and vermifuge.