<unk>  is an agricultural product processed from the fresh leaves of plants in the genus Nicotiana.<unk>  has been growing on the American Continent since about 6000 BC and began being used by native cultures at about 3000 BC. It has been smoked in one form or another since about 2000 BC.  There are pictoral drawings of ancient Mayans smoking crude cigars from 1400 BC.<unk>  has a very long history of use in Native American culture and played an important part in the foundation of the United States of America, going back to colonial times and the original Jamestown settlement.
Commercially available dried, cured and natural forms, it is often smoked (see<unk>  smoking) in the form of a cigar or cigarette, or in a stem pipe, water pipe, or hookah.<unk>  can also be chewed, "dipped" (placed between the cheek and gum), or sniffed into the nose as finely powdered snuff. Many countries set a minimum smoking age, regulating the purchase and use of<unk>  products.
All methods of<unk>  consumption results in varying quantities of nicotine being absorbed into the user's bloodstream. Over time, tolerance and dependence develop. Absorption quantity, frequency, and speed seem to have a direct relationship with how strong a dependence and tolerance, if any, might be created.
Tobacco
Alcohol
Polychlorinated biphenyl
Allergen
Toxic metal
Carcinogen
Nitrobenzene
Polycyclic aromatic hydrocarbon