Nicotine is a chemical that is found naturally only in the leaves, seeds, and roots of the tobacco plant— Nicotiana tabacum. Tobacco, which is the dried leaf of the tobacco plant, has a unique distinction. It is one of the few substances legally available that can harm or even kill when used as the manufacturer intends.

Nicotine is an extremely potent poison. It has been known to be a poison since the 1800s, when scientists first extracted nicotine from tobacco. Experiments in the mid-1800s showed that a few drops in the mouth would instantly kill a small animal like a cat.

For years, nicotine was used as an agricultural insecticide. In larger amounts, nicotine can poison humans. Too much nicotine can cause rapid pulse, vomiting, collapse, and even death. In the small amounts that are in tobacco, nicotine will not cause...