Why this poison is interesting

Nicotine is the rare poison that produces two opposite clinical pictures through a single receptor, in sequence, in the same patient. It is an agonist at the nicotinic acetylcholine receptor — the receptor found in the central and autonomic nervous systems, the neuromuscular junctions, and the adrenal medulla¹ — and at low dose it fires all of them. At high dose it does something a simple agonist should not: it holds the receptor depolarised, so that after the initial burst of firing the synapse falls silent and cannot be re-excited. The poisoning therefore runs biphasic¹: an early storm of stimulation, then a late collapse into blockade.

This makes nicotine the completion of a small family the library already has. The review that anchors this page groups the nicotinic alkaloids together — nicotine from tobacco, coniine from hemlock, cytisine from laburnum — because they act agonistically at nicotinic-type acetylcholine… receptors and presenting patients therefore have comparable toxidromes.¹ Hemlock and laburnum are already in this library as botanical entries; nicotine is the same mechanism reaching the emergency department far more often, through cigarettes, nicotine replacement and — the modern danger — vaping liquid.

It is also the library's clearest case of a lethal-dose figure that everyone quotes and no one can source. The number in every textbook — about 60 mg, or roughly 30–60 mg, as the fatal human oral dose — was traced back and found to rest on dubious self-experiments in the nineteenth century²; the true oral lethal-dose figure is considerably higher. That matters clinically, because the myth drives over-triage of trivial exposures while the genuinely dangerous ones — concentrated e-liquid in a small child — are newer than the folklore. A 15-month-old who swallowed e-liquid arrested and died of anoxic brain injury, with a urinary cotinine of 1,716 ng/mL.³

A poison is a drug whose kinetics have escaped its pharmacology.

The toxic principle

The toxic principle is nicotine acting at the nicotinic acetylcholine receptor. Because that receptor is deployed at so many sites, the effect is not confined to one system: the nicotinic-type acetylcholine receptor can vary both in its subunit composition and in its distribution within the body… agonistic interaction at these variable sites may explain why the alkaloids have diverse effects depending on the administered dose and duration of exposure.¹ The autonomic ganglia carry both sympathetic and parasympathetic outflow, and nicotine fires both — which is why the early picture mixes adrenergic signs (hypertension, tachycardia) with cholinergic ones (salivation, vomiting, sweating).

The dose-dependence is the mechanism's signature. At low occupancy nicotine is a straightforward agonist and the effect is stimulation. As occupancy rises the receptor is held depolarised — the same phenomenon that makes a depolarising neuromuscular blocker like suxamethonium paralyse after an initial fasciculation — and the synapse can no longer transmit. At the neuromuscular junction this produces fasciculation and then flaccid paralysis; at the ganglia, initial firing and then blockade; in the medulla, a catecholamine surge and then failure. One receptor, one molecule, and a clinical course that reverses direction as the concentration climbs. Established

Toxicokinetics

Nicotine's kinetics are those of a small lipophilic base that goes everywhere quickly and leaves reasonably fast: absorbed by every route, distributed widely including into brain and across the placenta, metabolised in the liver to cotinine and excreted renally. The route and the preparation, more than the kinetics, decide how dangerous a given exposure is.

Nicotine — absorbed everywhere, distributed everywhere, cleared reasonably fast
Parameter	Therapeutic	In overdose	Why it changes
Absorption	Absorbed readily across all routes — oral, buccal, respiratory, dermal¹; buccal and pulmonary absorption is fastest; gastric absorption is limited by the acidic pH and by vomiting	Route decides speed and danger: inhaled and buccal fast, swallowed slower and often vomited	The preparation matters more than the milligrams. E-liquid and gum deliver a bioavailable dose; a swallowed cigarette delivers less and provokes protective vomiting. This is why exposure history must specify the product, not just 'nicotine'.
Distribution	Rapidly and widely distributed, readily traversing the blood–brain barrier and the placenta, and into breast milk¹	Reaches its central and neuromuscular targets fast	The rapid CNS penetration is why the early stimulation and the late depression are both prompt, and why a large e-liquid ingestion can go from storm to collapse within a short window.
Metabolism	Predominantly in the liver¹, chiefly by CYP2A6, to cotinine and other metabolites	Cotinine is far less pharmacologically active than nicotine	Cotinine is the reason there is no toxic-metabolite story here — the main metabolite is a marker, not a poison, and it is what laboratories measure to confirm and quantify exposure.³
Elimination	Followed by rapid renal elimination¹; short half-life (of the order of a couple of hours for nicotine)	Fast enough that survivors of the acute phase clear the drug quickly	The short half-life is why supportive care works and extracorporeal removal is unnecessary — a patient supported through the biphasic course clears nicotine faster than a dialysis circuit would add anything.
Dialysability	—	Not indicated. Rapid distribution and hepatic clearance with a short half-life leave no role for extracorporeal removal	There is no EXTRIP recommendation and no rationale: the danger is the acute receptor effect, over within hours, and it is managed by supporting the airway and circulation rather than by removing the drug.

Metabolism and the metabolites

The metabolism is short and, for once, not where the toxicity lives. Nicotine is metabolised predominantly in the liver, chiefly by CYP2A6, to cotinine and a set of minor metabolites, and cotinine is far less active than the parent. There is no bioactivation: the poison is nicotine, the metabolite is a marker. Cotinine's only clinical role is diagnostic — it is what a laboratory measures to confirm and gauge an exposure, as in the fatal paediatric case where the urinary cotinine was 1,716 ng/mL.³

Nicotine — one receptor, then hepatic clearance to an inactive marker

NicotinenAChR agonist → depolarising blocker as occupancy rises¹
nicotinic acetylcholine receptors (CNS, ganglia, NMJ, adrenal medulla)Stimulation then depolarising block — the biphasic poisoning¹
Cotinine (+ minor metabolites)Far less active than nicotine — a marker, not a poison; measured to confirm exposure³
Urine (nicotine and cotinine)¹Short half-life; survivors of the acute phase clear the drug quickly

Elimination and accumulation

Nicotine is cleared quickly by hepatic metabolism and renal excretion, with a half-life of a couple of hours, so it does not accumulate in the way a renally cleared or long-half-life poison does. The clinical corollary is that the whole of the danger is compressed into the acute phase: a patient who survives the transition from stimulation to blockade, with the airway and circulation supported, is clearing the drug the entire time and does not face a delayed second insult from a metabolite.

Repeated or continuous exposure — a nicotine patch left on, ongoing dermal contact in green tobacco sickness — can prolong the stimulatory picture, because absorption continues; removing the source is part of the management for those routes.¹ But this is continued dosing rather than true accumulation of a persistent poison. Inferred

Target organs — and why those

Neuromuscular junction and respiratory muscles

TargetNicotinic (muscle-type) acetylcholine receptors held depolarised

Why hereThe organ that kills. As occupancy rises, the muscle nAChR depolarises and blocks — fasciculation, then flaccid paralysis — and when the diaphragm and intercostals are affected the patient cannot breathe. This is the depolarising-block half of the biphasic course, leading to… respiratory failure.¹ The neuromuscular junction is targeted because nicotine is, at high dose, a depolarising blocker there — the same class of action as suxamethonium, without the anaesthetist's control. Established

At the bedsideFasciculation and tremor early, then weakness and flaccid paralysis with respiratory failure — the indication for airway control and ventilation.¹

Autonomic ganglia and the cardiovascular system

TargetGanglionic nAChRs carrying both sympathetic and parasympathetic outflow

Why hereThe organ that produces the confusing, changing vital signs. Firing both autonomic limbs gives the early hypertension and tachycardia of adrenergic dominance; ganglionic blockade then gives the late hypotension and bradycardia.¹ The cardiovascular picture reverses because the ganglion first fires and then blocks — the same mechanism, read out through the autonomic nervous system. Established

At the bedsideHypertension and tachycardia early; hypotension and bradycardia late.¹ The reversal, without any change in dose, is the diagnostic clue and the danger signal.

Brain

TargetCentral nAChRs and, indirectly, the medullary respiratory and vomiting centres

Why hereIncluded because it drives both the early and the terminal features. Central nicotinic stimulation causes agitation, tremor and seizures and triggers the potent vomiting that limits oral absorption; central depression then contributes to the coma of the second phase.¹ The brain is targeted because nicotine crosses the blood–brain barrier readily¹ and acts on the same receptor centrally as peripherally. Established

At the bedsideAgitation, tremor, headache and vomiting early; seizures in severe poisoning; coma in the inhibitory phase.¹

Timeline of effects

Nicotine — the biphasic course: an early storm that can reverse into a late collapse

Time

What you seeWhat is happening

MinutesOnset
What you seeNausea, prominent vomiting, salivation, abdominal pain, tremor, agitation.¹
What is happeningRapid absorption and CNS penetration; nicotinic stimulation across ganglia, NMJ and brain. Vomiting is protective for oral exposures and limits what is absorbed.
Phase 1 — earlyStimulation
What you seeHypertension, tachycardia, tremors, fasciculation; agitation and, in severe cases, seizures.¹
What is happeningAgonist firing of nicotinic receptors — the adrenergic and cholinergic storm. Alarming but usually not the lethal phase.
Phase 2 — delayedDepolarising block
What you seeHypotension, bradycardia, dyspnoea, weakness and flaccid paralysis, coma, respiratory failure.¹
What is happeningAs receptor occupancy rises the synapse is held depolarised and blocks. The neuromuscular block causes respiratory failure; the ganglionic block causes the cardiovascular collapse. This is the phase to anticipate and support.
HoursClearance and recovery
What you seeRecovery is the rule for those supported through the acute phase; deaths are from early respiratory failure or arrest.¹³
What is happeningShort half-life and hepatic clearance to inert cotinine; no delayed metabolite injury. The whole danger is in the first hours.

What the mechanism predicts at the bedside

Anticipate the second phase. A patient who is agitated, hypertensive and tachycardic can progress to hypotension, bradycardia and respiratory failure without taking anything more¹; the airway and ventilation must be ready before that transition.
Ask what product, not just 'nicotine'. Concentrated e-liquid is the dangerous exposure and has killed a toddler³; a swallowed cigarette usually provokes protective vomiting and absorbs poorly. The preparation decides the risk.
Do not use the 60 mg lethal-dose figure to risk-assess. It is a myth traced to nineteenth-century self-experiments and is far too low²; over-reliance on it both over-triages trivial exposures and understates the danger of a large e-liquid ingestion. Risk-assess with TOXBASE and NPIS.
Support, do not remove. Airway protection, ventilation and circulatory support carry the patient through the biphasic course; the short half-life means dialysis adds nothing and none is indicated.¹
Atropine is for the muscarinic overflow, not the block. Bronchorrhoea, salivation and bradycardia from ganglionic parasympathetic firing can respond to atropine¹; it does nothing for the depolarising neuromuscular block, which needs ventilation. See atropine.
Treat seizures with benzodiazepines and the early hypertension, if severe, with short-acting agents — but expect both to be self-limiting as the phase turns.
Remove the source for continued exposures. Take off a nicotine patch, wash dermal contamination (green tobacco sickness)¹ — absorption continues until the source is gone.
Consider charcoal after a significant ingestion, weighing it against the vomiting the poison itself causes.¹ See activated charcoal.

The antidote, from the poison's side

There is no antidote, and the review is explicit that supportive care is the mainstay of management with primary emphasis on cardiovascular and respiratory support to ensure recovery.¹ The mechanism explains why: the lethal event is a depolarising neuromuscular block, and the only thing that reverses a receptor held depolarised is time and clearance — which the short half-life provides, if the patient is ventilated through it.

Airway and ventilatory support: The decisive intervention. The second phase paralyses the respiratory muscles¹; intubation and ventilation carry the patient across the depolarising block until nicotine is cleared. Everything else is secondary to this.
Atropine: For the muscarinic component of the stimulatory phase — bronchorrhoea, salivation, bradycardia from ganglionic parasympathetic firing. It treats the secretions and the vagal bradycardia, not the nicotinic neuromuscular block. See atropine.
Benzodiazepines: For seizures and agitation in the stimulatory phase — a GABA-ergic brake on a nicotinically over-driven CNS.
Activated charcoal: Considered after a significant ingestion, adsorbing nicotine, and weighed against the vigorous vomiting the poison already causes.¹ See activated charcoal.
Source removal: Specific to the continuous routes: remove a nicotine patch, decontaminate skin after dermal exposure.¹ Absorption continues while the source is in contact.
Extracorporeal removal: No role. Rapid distribution, hepatic clearance and a short half-life mean supportive care outpaces any circuit; there is no EXTRIP recommendation.

Critical appraisal

The 60 mg lethal dose is downgraded to Traditional teaching with a citation for the doubt. Mayer's analysis traced the generally accepted figure to dubious self-experiments in the nineteenth century² and concluded the true oral lethal dose is much higher. This is a genuine downgrade of a received number, supported by a paper that contests it directly — exactly the condition the house style requires, and not a manufactured doubt.
The biphasic mechanism is Established. Agonism at nicotinic receptors followed by depolarising block is standard receptor pharmacology and is the review's central claim¹; the Established badges reflect that, while the route-specific absorption arguments (e-liquid vs swallowed cigarette) are badged Inferred as the standard explanation rather than a measured comparison.
The severity and fatality data are case-level. The paediatric e-liquid death³ is one well-documented case with a confirmatory cotinine; it establishes that a small e-liquid ingestion can be fatal in a child, not a dose–response, and the page claims the former.
Pharmacokinetic specifics are quoted at the level the sources support. The review gives the qualitative kinetics — all-route absorption, wide distribution, hepatic metabolism, rapid renal elimination¹; the CYP2A6 route and the ~2-hour half-life are standard pharmacology added for completeness, and the page does not build a dosing argument on them.
No lethal dose is given, deliberately. The whole point of the Mayer citation is that the widely quoted figure is unreliable²; the page therefore states that a concentrated e-liquid ingestion can be dangerous and refers risk assessment to TOXBASE and NPIS rather than substituting a new number for a discredited one.
Green tobacco sickness and NRT toxicity are named but not quantified. They are included to complete the exposure routes¹; their individual severity is not the subject of the cited evidence and is not asserted here.

References

1
Schep LJ, Slaughter RJ, Beasley DM. Nicotinic plant poisoning. Clinical Toxicology (Phila) 2009 Sep;47(8):771–781. PMID 19778187. Systematic review grouping nicotine, coniine (hemlock) and cytisine (laburnum) as nicotinic-receptor agonists with a shared, biphasic toxidrome — early cholinergic stimulation, delayed inhibitory blockade with hypotension, bradycardia and respiratory failure; supportive care the mainstay.
2
Mayer B. How much nicotine kills a human? Tracing back the generally accepted lethal dose to dubious self-experiments in the nineteenth century. Archives of Toxicology 2014 Jan;88(1):5–7. PMID 24091634. Traces the widely quoted human lethal-dose figure (about 60 mg) to unreliable nineteenth-century self-experiments and argues the true figure is considerably higher.
3
Seo AD, Kim DC, Yu HJ, Kang MJ. Accidental ingestion of E-cigarette liquid nicotine in a 15-month-old child: an infant mortality case of nicotine intoxication. Korean Journal of Pediatrics 2016 Dec;59(12):490–493. PMID 28194215. A toddler who ingested e-liquid arrested and died of anoxic brain injury, with a urinary cotinine of 1,716 ng/mL — the modern paediatric hazard of concentrated nicotine solutions.

Nicotine

At a glance