smoked (Tobacco smoking) (as smoking tobacco, mapacho, etc.), insufflate (Insufflation (medicine))d (as tobacco snuff or nicotine nasal spray), chewed (Chewing) (as nicotine gum, tobacco gum or chewing tobacco), transdermal (Nicotine patch) (as nicotine patch, nicogel or topical tobacco paste), intrabuccal (as dipping tobacco, snuffs, dissolvable tobacco or creamy snuff), vaporized (as electronic cigarette, etc.), directly inhaled (as nicotine inhaler), oral (as nicotini) dependency_liability = Medium to high

Nicotine is an alkaloid found in the nightshade family of plants (Solanaceae) that constitutes approximately 0.6-3.0% of dry weight of tobacco, with biosynthesis taking place in the roots and accumulation occurring in the leaves. It functions as an antiherbivore chemical (Plant defense against herbivory) with particular specificity to insects; therefore nicotine was widely used as an insecticide in the past, and currently nicotine analogs such as imidacloprid continue to be widely used.

In low concentrations (an average cigarette yields about 1 mg of absorbed nicotine), the substance acts as a stimulant in mammals and is the main factor responsible for the dependence-forming properties of tobacco smoking. According to the American Heart Association, the "nicotine addiction (Substance_use_disorder) has historically been one of the hardest addictions to break." The pharmacological and behavioral characteristics that determine tobacco addiction are similar to those that determine addiction to drugs such as heroin and cocaine. Nicotine content in cigarettes has slowly increased over the years, and one study found that there was an average increase of 1.6% per year between the years of 1998 and 2005. This was found for all major market categories of cigarettes.