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 CHN. 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 it can be a tranquilizer when inhaled slowly and deeply. In larger doses nicotine is a highly toxic poison, used as an insecticide, fumigant, and vermifuge.
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