Nicotine is a potent parasympathomimetic alkaloid found in the nightshade family of plants and is a stimulant drug.
Nicotine is a nicotinic acetylcholine receptor (nAChR) agonist, except at nAChRα9 and nAChRα10 where it acts as an antagonist. It is made in the roots of and accumulates in the leaves of the nightshade family of plants. Nicotine is found in the leaves of Nicotiana rustica in amounts of 2–14%, the tobacco plant Nicotiana tabacum, Duboisia hopwoodii and Asclepias syriaca.
It constitutes approximately 0.6–3.0% of the dry weight of tobacco and is present in the range of 2–7 µg/kg of various edible plants. It functions as an antiherbivore chemical; consequently, nicotine was widely used as an insecticide in the past and neonicotinoids such as imidacloprid are currently widely used.
Nicotine is addictive. In lesser doses (an average cigarette yields about 2 mg of absorbed nicotine), the substance acts as a stimulant in mammals, while high amounts (50–100 mg) can be harmful. This stimulant effect is a contributing factor to the addictive properties of tobacco smoking. Nicotine's addictive nature includes psychoactive effects, drug-reinforced behavior, compulsive use, relapse after abstinence, physical dependence and tolerance.
Nicotine is associated with cardiovascular disease, potential birth defects, and poisoning. In vitro studies have associated it with cancer, but carcinogenicity has not been demonstrated in vivo. There is inadequate research to demonstrate that nicotine is associated with cancer in humans ,Medicinal nicotine as a tool to quitting smoking has a good safety history. During pregnancy, there are risks to child later in life for type 2 diabetes, obesity, hypertension, neurobehavioral defects, respiratory dysfunction, and infertility. Nicotine is regarded as a potentially lethal poison. It is unlikely that a person would overdose on nicotine through smoking alone. The use of electronic cigarettes, which are designed to be refilled with nicotine-containing e-liquid, has renewed interest in nicotine overdoses, especially with regard to the possibility of young children ingesting the liquids.
Nicotine is regarded as a potentially lethal poison. The LD50 of nicotine is 50 mg/kg for rats and 3 mg/kg for mice. 30–60 mg (0.5–1.0 mg/kg) can be a lethal dosage for adult humans. However the widely used human LD50 estimate of 0.5–1.0 mg/kg was questioned in a 2013 review, in light of several documented cases of humans surviving much higher doses; the 2013 review suggests that the lower limit causing fatal outcomes is 500–1000 mg of ingested nicotine, corresponding to 6.5–13 mg/kg orally. Nevertheless, nicotine has a relatively high toxicity in comparison to many other alkaloids such as caffeine, which has an LD50 of 127 mg/kg when administered to mice.
Today nicotine is less commonly used in agricultural insecticides, which was a main source of poisoning. More recent cases of poisoning typically appear to be in the form of Green Tobacco Sickness or due to accidental ingestion of tobacco or tobacco products or ingestion of nicotine containing plants.
People who harvest or cultivate tobacco may experience Green Tobacco Sickness (GTS), a type of nicotine poisoning caused by dermal exposure to wet tobacco leaves. This occurs most commonly in young, inexperienced tobacco harvesters who do not consume tobacco. People can be exposed to nicotine in the workplace by breathing it in, skin absorption, swallowing it, or eye contact.
The Occupational Safety and Health Administration (OSHA) has set the legal limit (permissible exposure limit) for nicotine exposure in the workplace as 0.5 mg/m3 skin exposure over an 8 hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 0.5 mg/m3 skin exposure over an 8 hour workday. At levels of 5 mg/m3, nicotine is immediately dangerous to life and health.
It is unlikely that a person would overdose on nicotine through smoking alone, the US Food and Drug Administration (FDA) states in 2013 "There are no significant safety concerns associated with using more than one OTC NRT at the same time, or using an OTC NRT at the same time as another nicotine-containing product
—including a cigarette."
The recent rise in the use of electronic cigarettes, many forms of which are designed to be refilled with nicotine-containing e-liquid supplied in small plastic bottles, has renewed interest in nicotine overdoses, especially in the possibility of young children ingesting the liquids. A 2015 report on e-cigarettes by Public Health England noted an "unconfirmed newspaper report of a fatal poisoning of a two-year old child" and two published case reports of children of similar age who had recovered after ingesting e-liquid and vomiting. They also noted case reports of suicides by nicotine. Where adults drank liquid containing up to 1,500 mg of nicotine they recovered (helped by vomiting), but an ingestion apparently of about 10,000 mg was fatal, as was an injection. They commented that "Serious nicotine poisoning seems normally prevented by the fact that relatively low doses of nicotine cause nausea and vomiting, which stops users from further intake."