A

David

Darling

nicotine

structure of the nicotine molecule

Nicotine is an alkaloid occurring in tobacco leaves and extracted from tobacco refuse. It is a colorless, oily liquid. Nicotine is used as an insecticide and to make niacin (nicotinic acid). It is one of the most toxic substances known; even the small doses ingested by smoking causes blood-vessel constriction, raised blood pressure, nausea, headache, and impaired digestion.