What is nicotine?

As written in the 1994 edition of Miller-Keane’s Encyclopedia & Dictionary of Medicine, Nursing, & Allied Health, Fifth Edition:

NICOTINE — a very poisonous alkaloid that in its pure state is a colorless, pungent, oily liquid, having an acrid burning taste. It is a constituent of tobacco, and is produced synthetically. In water solution, it is sometimes used as an insecticide and plant spray.

Although nicotine is highly toxic, the amount inhaled while smoking tobacco is too small to cause death (most of the nicotine is burned off).

The nicotine in tobacco can, however, cause indigestion and increase in blood pressure, and dull the appetite. It also acts as a vasoconstrictor (constricting the blood vessels.) Smoking often leads to heart disease, stroke, lung cancer, asthma, and other diseases.