Tobacco is a product prepared from the leaves of the tobacco plant by curing them. The plant is part of the genus Nicotiana and of the Solanaceae (nightshade) family. While more than 70 species of tobacco are known, the chief commercial crop is N. tabacum. The more potent variant N. rustica is also used around the world.
Tobacco contains the alkaloid nicotine, which is a stimulant, and harmala alkaloids. Dried tobacco leaves are mainly used for smoking in cigarettes, cigars, pipe tobacco, and flavored shisha tobacco. They can also be consumed as snuff, chewing tobacco, dipping tobacco and snus.
Tobacco use is a risk factor for many diseases, especially those affecting the heart, liver, and lungs, as well as many cancers. In 2008, the World Health Organization named tobacco as the world's single greatest preventable cause of death.