Nicotine is a chiral alkaloid that is naturally produced in the nightshade family of plants (most predominantly in tobacco and Duboisia hopwoodii)[6] and is widely used recreationally as a stimulant and anxiolytic. As a pharmaceutical drug, it is used for smoking cessation to relieve withdrawal symptoms.[7][4][8][9] Nicotine acts as a receptor agonist at most nicotinic acetylcholine receptors (nAChRs),[10][11][12] except at two nicotinic receptor subunits (nAChRα9 and nAChRα10) where it acts as a receptor antagonist.[10]
Nicotine constitutes approximately 0.6–3.0% of the dry weight of tobacco.[13] Nicotine is also present at ppb-concentrations in the edible family Solanaceae, including potatoes, tomatoes, and eggplants,[14] though sources disagree on whether this has any biological significance to human consumers.[14] It functions as an antiherbivore chemical; consequently, nicotine was widely used as an insecticide in the past,[15][16]and neonicotinoids, such as imidacloprid, are some of the most effective and widely used insecticides.
Nicotine is highly addictive[17][18][19] unless used in slow-release forms.[20][21][22]Animal research suggests that monoamine oxidase inhibitors present in tobacco smoke may enhance nicotine's addictive properties.[23][24] Denicotinized tobacco acutely reduces nicotine withdrawal,[25][26] raises striatal dopamine[27] and is also investigated as add on therapy to standard therapy to quit smoking.[28] An average cigarette yields about 2 mg of absorbed nicotine.[29] The estimated lower dose limit for fatal outcomes is 500–1,000 mg of ingested nicotine for an adult (6.5–13 mg/kg).[23][29] Nicotine addiction involves drug-reinforced behavior, compulsive use, and relapse following abstinence.[30] Nicotine dependence involves tolerance, sensitization,[31] physical dependence, and psychological dependence.[32] Nicotine dependence causes distress.[33][34] Nicotine withdrawal symptoms include depressed mood, stress, anxiety, irritability, difficulty concentrating, and sleep disturbances.[1]Mild nicotine withdrawal symptoms are measurable in unrestricted smokers, who experience normal moods only as their blood nicotine levels peak, with each cigarette.[35] On quitting, withdrawal symptoms worsen sharply, then gradually improve to a normal state.[35]
Nicotine use as a tool for quitting smoking has a good safety history.[36] Animal studies suggest that nicotine may adversely affect cognitive development in adolescence, but the relevance of these findings to human brain development is disputed.[37][23] At low amounts, it has a mild analgesic effect.[38] According to the International Agency for Research on Cancer, "nicotine is not generally considered to be a carcinogen."[39][40] 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 nicotine and risk for cancer.[41] Nicotine has been shown to produce birth defects in some animal species, but not others.[42] It is considered a teratogen in humans.[43] The median lethal dose of nicotine in humans is unknown,[44] but high doses are known to cause nicotine poisoning.[41]
https://en.wikipedia.org/wiki/Nicotine
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