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 C 10 H 14 N. 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.