Nicotine is a chemical substance found in the tobacco plant and its products, including cigarettes, cigars, pipe tobacco, and smokeless tobacco (such as chewing tobacco and snuff). People who smoke cigarettes or use tobacco in other ways can become addicted to the nicotine contained in these products.

Nicotine can occur in two forms. The active form, called L- nicotine, is found in tobacco plants of the genus Nicotiana. These plants belong to the nightshade family (Solanaceae). Nicotiana plants, especially Nicotiana tabacum, were grown for their leaves in South America before the arrival of Christopher Columbus. The inactive form of nicotine, D-nicotine, is not present in tobacco leaves. Instead, a small amount forms when tobacco is burned during smoking. In addition to tobacco plants, small amounts of nicotine are found in foods of the nightshade family, such as tomatoes and eggplants. Nicotine that has been extracted from tobacco leaves...