Nicotine

Nicotine
Nicotine molecular structure
Formula	C₁₀H₁₄N₂
Type	Alkaloid (parasympathomimetic stimulant)
Administration	Transdermal (patch), buccal (gum, pouch, lozenge), inhaled, sublingual
Solubility	Freely soluble in water; miscible with alcohol and ether. pKa ~8.0 (basic, so alkaline pH improves absorption)
Legal status	18/21+, OTC (nicotine replacement products); regulated in tobacco products; prescription in some countries
Synonyms	3-(1-Methyl-2-pyrrolidinyl)pyridine; (S)-nicotine; 1-Methyl-2-(3-pyridyl)pyrrolidine, Cigarettes, Tobacco, Zyn, Vape
Bioavailability	Oral: ~20% (due to first-pass metabolism); Transdermal: ~68-82%; Gum: 50-80%; Inhaled: ~51-56%
Recommended dose	1-2 mg daily for cognitive/metabolic effects (non-smokers); NRT: 2-4 mg gum/lozenges, 7-21 mg patches
Upper limit	Varies by individual; acute toxicity symptoms appear around 40-60 mg in adults. Conservative guidance suggests keeping daily use below 20 mg
LD50	Mice (IP): ~10 mg/kg; Mice (oral): ~23-33 mg/kg; Human estimated: ~0.5-1.0 mg/kg (contested; may be higher)
Ray's verdict	Depends on context Age-dependent: cautiously supportive in older age, mainly at low doses; the main danger is the smoke, not the nicotine itself.

Nicotine's effects are age-dependent. In older people, low-dose nicotine can improve alertness and probably protect nerves, consistent with the inverse association between smoking and Parkinson's disease; in younger people, its vasoconstrictive effect tends to promote skin wrinkling and probably contributes to periodontal disease. After middle age, nicotine isn't likely to become addictive, and small amounts have nerve-protective effects that overlap with those of niacinamide.

Structure/Chemical properties

Nicotine is a pyridine alkaloid. Cotinine, nicotine's main tobacco-leaf-associated metabolite, is structurally similar to nicotine itself.

Function/Mechanism of action

Nicotine is a direct agonist of nicotinic acetylcholine receptors; this direct cholinergic activation, rather than its being a "poison," is the main mechanism behind both its benefits and its risks; it can support an anti-inflammatory pathway or, in the wrong context, activate cancer metabolism instead.

At low doses, equivalent to about 1-2 mg daily (roughly half a cigarette), nicotine is a powerful aromatase inhibitor and, through the same MAO-B inhibition seen with other catatoxic agents, supports dopamine tone; those effects, along with cotinine's, shift toward activating the adrenergic/sympathetic system instead once the dose is exceeded. Most people using nicotine gums or patches consume drastically more than that protective equivalent dose, which quickly turns nicotine into a stress agent rather than a protective one.

Nicotine is also among the substances known to protect against excitotoxic calcium overload, the mechanism implicated in ALS, Alzheimer's disease, Parkinson's disease, Huntington's chorea, and epilepsy, alongside magnesium and progesterone.

Schizophrenia patients are almost always heavy smokers; nicotine's brain-protective, anti-inflammatory effect against degenerative disease probably overlaps with niacin's own role as an energy-supporting, anti-inflammatory, nerve-protective nutrient. Asked directly whether nicotine overlaps with nicotinamide specifically, though, Peat said he hadn't encountered any such overlap.

A meta-analysis found Parkinson's disease risk was roughly 60% lower in smokers than in never-smokers, consistent with the dopaminergic and MAO-B-inhibiting mechanisms described above. Smoking is also associated with dose-dependently higher testosterone: a systematic review and meta-analysis found heavier smokers had higher serum testosterone than lighter smokers or nonsmokers, and nicotine, cotinine, and anabasine directly inhibit aromatase in human trophoblast tissue, backing up the low-dose aromatase-inhibiting effect already noted above.

Smoking also raises 24-hour energy expenditure by about 10%, an effect that may partly explain the weight gain often seen after quitting. Consistent with the low-dose framing above, a systematic review found no significantly increased all-cause or smoking-related mortality among people smoking only 1-2 cigars per day, unlike heavier cigar use or cigarette smoking.

Medical uses/Effects

Benefits

• In older people, low-dose nicotine improves alertness and probably protects nerves.
• Animal studies showing protection against Parkinson's disease, Alzheimer's disease, heart disease, and cancers used doses equivalent to about 1-2 mg daily, roughly half a cigarette.
• Nicotine is significantly protective against Parkinson's disease specifically, per a substantial body of research.
• Protects against excitotoxic calcium overload implicated in several major neurodegenerative diseases.

Risks and dose-dependence

In younger people, nicotine's vasoconstrictive effect promotes skin wrinkling and probably contributes to periodontal disease. Chronic use raises free fatty acids and triggers adrenergic/cortisol stress responses, which can impair metabolism long-term; once typical nicotine-replacement doses (well above the ~1-2 mg/day protective equivalent) are reached, the same receptor activation that is protective at low doses becomes a stress agent instead. Because nicotine's main risk is direct activation of the cholinergic receptor system, its effects on any given person's inflammatory or metabolic state aren't fully predictable; it has the potential to help but can instead activate cancer metabolism.

Dosing

The carbon monoxide isn't likely to be absorbed in dangerous amounts if the smoke isn't inhaled. I think the safest way to use tobacco is either transdermally or orally; it has a laxative and anti-inflammatory effect.

— Ray Peat

The doses used in animal studies showing protection against Parkinson's, Alzheimer's, heart disease, and cancer were equivalent to only about 1-2 mg daily, roughly half a cigarette; most nicotine gum or patch users take drastically more than that. Peat preferred absorbing nicotine through the skin (as an ointment) or ingesting very small amounts of tobacco leaf directly over smoking; nicotine itself is a neurotoxin, but it isn't the main poisonous component of tobacco smoke.

Lobelia's active compound, lobeline, occupies the nicotinic receptor without being nicotine itself, and has also been used to help people stop smoking.

Side/Adverse effects

Nicotine can help correct inflammatory processes at the right dose, but the same direct cholinergic receptor activation that can be protective can instead activate cancer metabolism; the balance depends heavily on dose and context rather than nicotine being simply good or bad.

Aging and NAD+

Low-dose nicotine has been shown to improve aging-related symptoms in animal models. A 2023 study in male mice found that nicotine rebalanced NAD+ homeostasis by enhancing NAMPT activity, leading to improved mitochondrial function, increased NAD+ levels, upregulation of SIRT1, and amelioration of age-related metabolic and physical decline. This is distinct from the harmful effects of smoking, and suggests nicotine's pro-metabolic effects at low doses (aromatase inhibition, MAO-B inhibition, cholinergic stimulation) may extend to the NAD+/sirtuin axis.

Gut effects

Nicotine accumulates in gastric juice, reduces gastric mucosal blood flow, inhibits PGE2, and impairs mucosal cytoprotection. For people with existing gut issues, such as SIBO, leaky barrier, or endotoxin-driven inflammation, cutting back on nicotine may do more for gut health than many supplements aimed at the same problem. This effect is dose-dependent and more pronounced with oral/tobacco forms than with transdermal nicotine replacement.

Endotoxin and systemic inflammation

Transdermal nicotine pretreatment attenuates the febrile, cardiovascular, and cytokine responses to intravenous bacterial endotoxin (LPS) in healthy humans, with elevated cotinine throughout the challenge and a shift toward higher circulating IL-10 and cortisol, consistent with a blunted systemic inflammatory response. This LPS-attenuation effect is distinct from smoking's carcinogenic combustion products and supports a mechanism in which nicotine's anti-inflammatory action, including against endotoxin-driven cascades, may partly account for epidemiological associations between tobacco use and altered inflammatory-disease risk.

Harm reduction

PUFA interaction: Smoking releases polyunsaturated fatty acids into the bloodstream and oxidizes them, reducing plasma levels of linoleic and arachidonic acids and leading to elevated oxidative stress that promotes vascular damage and disease.

For people trying to quit smoking, careful use of nicotine gum together with belladonna (to block some of nicotine's circulatory side effects) can allow a person to overcome the behavioral habit of handling cigarettes and avoid the worst toxins of smoke, without also having to modify the chemical addiction at the same time; caffeine and vitamin A are protective against cancers caused by smoke exposure. Progesterone and pregnenolone have anti-toxic ("catatoxic") effects, though their effect specifically on nicotine craving is slight. Separately, a clinical study found women's naturally rising progesterone phase during the menstrual cycle raised odds of successful smoking abstinence on nicotine patches by about 37% versus a stable or falling phase. See Progesterone.

In commercial cigarettes, tobacco often contains sugar and/or glycerin additives. Non-organic tobacco introduces higher levels of heavy metals such as lead and cadmium from inorganic phosphate fertilizers; buying and shredding organic tobacco leaves avoids pesticides and reduces heavy-metal exposure.

Tobacco combustion produces carcinogens like benzene; these pyrolysis compounds share chemical components with those formed during food cooking. Switching from highly processed junk cigarettes to pure tobacco can change taste preference, which is itself evidence that the junk-cigarette additives are part of what's addictive.

More in Harm reduction.

Brands and sources

• Rolling tobacco
  • Pueblo blue rolling tobacco
  • American Spirit
• Cigarettes
• Patches
• Oral
• Supplemental