Physostigmine (Calabar Bean Alkaloid · AChE Inhibitor · Informational)
Compiled from published pharmacological and botanical literature. Not independently verified by Herbuno. Spotted an error or have a correction? Flag it below →
| Compound | Physostigmine (Eserine; Antilirium) |
| Chemical class | Alkaloid — Indole (pyrroloindole carbamate) |
| CAS | 57-47-6 |
| Primary source | Physostigma venenosum (Calabar bean), seeds |
| Key applications | Reversible acetylcholinesterase inhibitor; anticholinergic-toxicity antidote; glaucoma; informational-only |
| Claim strength | High (pharmaceutical) |
| Typical form | Pharmaceutical injectable / ophthalmic (physostigmine salicylate); not a supplement ingredient |
| Buy from Herbuno | Informational reference — see HerbIQ Compound Index → |
Name origin: Physostigmine is named directly for its source, Physostigma venenosum, the venenosum ("venomous") epithet marking the Calabar bean's toxicity; its older name, eserine, derives from a West African vernacular term for the bean. Structurally it is a pyrroloindole carbamate, and it is the carbamate group that carbamylates the active site of acetylcholinesterase to produce reversible enzyme inhibition. Traditional use: The Calabar bean was used in West African Efik culture as an ordeal poison — the accused would swallow a bean preparation, and survival or death was read as a verdict — a practice that inadvertently supplied a potent, reproducible source of cholinergic toxicity for later scientific study. British investigators introduced the bean to Europe in the mid-nineteenth century, and its active alkaloid became one of the earliest cholinergic agents to be systematically characterised. Research trajectory: Physostigmine effectively founded the pharmacology of cholinesterase inhibition and remains in clinical use as the antidote for central anticholinergic syndrome, where its capacity to cross the blood-brain barrier is decisive Blackstone 2020; toxicology-registry analyses describe its real-world use, effectiveness, and safety in anticholinergic toxidromes, including its association with reduced rates of intubation Watkins 2015. It also has a long ophthalmic history in glaucoma, where its miotic action lowers intraocular pressure. Safety context: Physostigmine has a narrow therapeutic window and can cause bradycardia, bronchospasm, seizures, and asystole in excess, so it is a monitored prescription drug rather than a supplement, and it is documented here as a reference only.
Evidence for Physostigmine Applications
Anticholinergic antidote: Physostigmine reversibly inhibits acetylcholinesterase, raising synaptic acetylcholine so that it out-competes antimuscarinic drugs at their receptors; because it is a tertiary amine it crosses into the CNS and reverses central as well as peripheral anticholinergic toxicity, which quaternary anticholinesterases cannot do Blackstone 2020. Toxicology-registry analysis of anticholinergic toxidromes found that patients treated with physostigmine had a significantly lower rate of intubation than those managed with benzodiazepines or supportive care alone Watkins 2015. Claim strength: High (pharmaceutical context).
Glaucoma and ophthalmic use: As a cholinergic agent, physostigmine constricts the pupil and facilitates aqueous outflow, lowering intraocular pressure; this established ophthalmic application predates modern glaucoma pharmacotherapy and is part of the compound's long clinical history. Claim strength: High (pharmaceutical context).
Cholinergic pharmacology probe: Physostigmine is a foundational tool compound for studying cholinergic neurotransmission and served as the structural template for later reversible carbamate anticholinesterases, some of which were developed for Alzheimer's disease and myasthenia gravis. Its well-defined, reversible mechanism makes it a reference inhibitor in enzymology. Claim strength: Moderate.
Safety-limiting cholinergic effects: The same acetylcholine accumulation that reverses anticholinergic toxicity can, in excess, produce a cholinergic crisis: bradycardia, hypersalivation, bronchospasm, seizures, and asystole. This is why dosing is cautious and incremental and why atropine is kept available as a countermeasure, and it is the core reason the compound is confined to monitored clinical use. Claim strength: High (pharmaceutical context).
Pharmacokinetics: Physostigmine is rapidly hydrolysed in vivo, with an elimination measured in roughly one to two hours, so its effect is transient and repeated dosing may be needed in prolonged anticholinergic toxicity — a kinetic feature central to how it is used clinically. Claim strength: Moderate.
This compound is documented for research and formulator education purposes. For commercially available botanical ingredients, explore the HerbIQ Compound Index →
Dosage & Formulator Specification
Physostigmine is a pharmaceutical antidote not appropriate for dietary-supplement formulation, and no consumer dosing applies. Clinical dosing for anticholinergic toxicity uses small milligram intravenous increments given slowly with continuous cardiac monitoring and atropine on hand to counter any cholinergic excess.
The Calabar bean (Physostigma venenosum) is a toxic botanical, not a food-safe supplement material, and its seeds carry the concentrated alkaloid. There is no supplement-grade physostigmine application, and formulators should regard the source plant as a pharmaceutical and toxicological reference rather than an ingredient.
Commercially, physostigmine is prepared as the salicylate salt for injection or ophthalmic use, with analytical control by HPLC against reference standards. Its rapid in-vivo hydrolysis and narrow therapeutic index place stringent demands on purity and dose accuracy in pharmaceutical manufacture, standards that have no counterpart in supplement production and underline why the compound sits outside the botanical-ingredient category.
This page documents physostigmine as a chemical-family and mechanistic reference within the HerbIQ index, situating it alongside other cholinergic-active alkaloids (such as galantamine and huperzine A elsewhere in the library) without implying any sourcing route.
Frequently Asked Questions — Physostigmine
What is physostigmine?
Physostigmine (eserine) is a reversible acetylcholinesterase-inhibiting alkaloid from the seeds of the Calabar bean, Physostigma venenosum. Because it is a tertiary amine that crosses the blood-brain barrier, it is used clinically as an antidote for central anticholinergic toxicity and historically in the management of glaucoma.
How does physostigmine work?
Physostigmine reversibly inhibits acetylcholinesterase, the enzyme that breaks down acetylcholine, so synaptic acetylcholine accumulates and cholinergic signalling is prolonged at both peripheral and central synapses. In anticholinergic poisoning this restored acetylcholine out-competes the offending antimuscarinic drug at its receptors and reverses the toxidrome.
Why is physostigmine informational-only?
It is a prescription antidote with a narrow therapeutic window and real cardiovascular risks, including bradycardia and, in overdose, seizures and asystole. It has no dietary-supplement application and appears in HerbIQ as a chemical-family reference.
What is the Calabar bean?
The Calabar bean (Physostigma venenosum) is a West African climbing legume whose seeds were historically used by the Efik people as an ordeal poison in trials of guilt or innocence. Nineteenth-century investigators isolated its principal toxic alkaloid, physostigmine, which became one of the earliest studied cholinergic agents and a template for later carbamate anticholinesterases.
Related compounds: Galantamine, Huperzine A, Reserpine, Pilocarpine
Claim-strength scale – High = multiple human RCTs; Moderate = limited trials or strong preclinical convergence; Emerging = early-stage lab or animal data.
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