Tobacco makes nicotine to poison the insects that try to eat it
Nicotine evolved as a plant's chemical weapon: to insects it is a potent neurotoxin. Farmers sprayed tobacco extracts on crops from at least 1690, and Americans bought it as a garden insecticide until 1992. The same molecule gave its name to the nerve receptor it targets, in bugs and in human brains alike.
Tobacco leaves carry roughly 0.6 to 3 percent nicotine by dry weight, and tomatoes, potatoes and aubergines, fellow members of the nightshade family, hold traces too. Purified, it is an oily liquid, colourless to yellowish, that slips easily through biological membranes. In the United States a nicotine sulfate product sold as Black Leaf 40 stayed on shelves from 1915 to 1992. The European Union banned nicotine pesticides in 2009, and the US followed in 2014, including on organic farms. Its chemistry lives on in the neonicotinoids such as imidacloprid, synthetic cousins that a plant absorbs throughout its tissues, so they cannot simply be rinsed away.
In people the molecule latches onto nicotinic acetylcholine receptors, triggering the release of dopamine, noradrenaline and acetylcholine. Users report sharper alertness, calmer nerves and a mild lift in mood. A 2010 meta-analysis of 41 placebo-controlled trials found measurable gains in fine motor skill, attention and working memory. Its tightest grip is on one receptor subtype, alpha-4 beta-2, which also drives its addictiveness. A typical cigarette delivers about 2 milligrams to the bloodstream.
Speed matters. The faster a dose reaches the brain, the more habit-forming it becomes, which is why patches and lozenges release it slowly while cigarettes deliver a rapid hit. Oddly, in animal experiments nicotine proves a fairly weak reinforcer compared with other addictive drugs, and researchers suspect other constituents of tobacco smoke, such as acetaldehyde, amplify its pull. Withdrawal symptoms tend to peak within one to three days. A 2018 Cochrane review found that every form of replacement therapy raised quitting success by 50 to 60 percent.
Neither the International Agency for Research on Cancer nor the US Surgeon General classes nicotine itself as a carcinogen; much of smoking's heart damage is linked to other smoke components such as carbon monoxide. Still, it raises heart rate and blood pressure, narrows blood vessels, disrupts sleep, can harm a developing fetus, and in large doses is a poison. As of 2024, about 1.2 billion people used tobacco products.
Source: Nicotine
