<unk>  is a naturally produced alkaloid in the nightshade family of plants (most predominantly in tobacco and Duboisia hopwoodii) and is widely used recreationally as a stimulant and anxiolytic. As a pharmaceutical drug, it is used for smoking cessation to relieve withdrawal symptoms.<unk>  acts as a receptor agonist at most<unk> c acetylcholine receptors (nAChRs), except at two<unk> c receptor subunits (nAChRα9 and nAChRα10) where it acts as a receptor antagonist.<unk>  constitutes approximately 0.6–3.0% of the dry weight of tobacco.<unk>  is also present at ppb-concentrations in edible plants in the family Solanaceae, including potatoes, tomatoes, and eggplants, though sources disagree on whether this has any biological significance to human consumers. It functions as an antiherbivore chemical; consequently,<unk>  was widely used as an insecticide in the past, and neonicotinoids, such as imidacloprid, are some of the most effective and widely used insecticides.<unk>  is highly addictive unless used in slow-release forms. Animal research suggests that monoamine oxidase inhibitors present in tobacco smoke may enhance<unk> 's addictive properties. Tobacco with reduced<unk>  (denicotinized tobacco) acutely reduces<unk>  withdrawal, raises striatal dopamine and is also investigated as add on therapy to standard therapy to quit smoking. An average cigarette yields about 2 mg of absorbed<unk> . The estimated lower dose limit for fatal outcomes is 500–1,000 mg of ingested<unk>  for an adult (6.5–13 mg/kg).<unk>  addiction involves drug-reinforced behavior, compulsive use, and relapse following abstinence.<unk>  dependence involves tolerance, sensitization, physical dependence, psychological dependence, and can cause distress.<unk>  withdrawal symptoms include depressed mood, stress, anxiety, irritability, difficulty concentrating, and sleep disturbances. Mild<unk>  withdrawal symptoms are measurable in unrestricted smokers, who experience normal moods only as their blood<unk>  levels peak, with each cigarette. On quitting, withdrawal symptoms worsen sharply, then gradually improve to a normal state.<unk>  use as a tool for quitting smoking has a good safety history. Animal studies suggest that<unk>  may adversely affect cognitive development in adolescence, but the relevance of these findings to human brain development is disputed. At low amounts, it has a mild analgesic effect. According to the International Agency for Research on Cancer,<unk>  is not generally considered to be a carcinogen." The Surgeon General of the United States indicates that evidence is inadequate to infer the presence or absence of a causal relationship between exposure to<unk>  and risk for cancer.<unk>  has been shown to produce birth defects in some animal species, but not others. It is considered a teratogen in humans. The median lethal dose of<unk>  in humans is unknown, but high doses are known to cause<unk>  poisoning.
Nicotine
Heroin
Cannabis 
Cannabis
Cocaine
Cocaine 
Benzyl alcohol
Methamphetamine