Scientific Name(s): Physostigma venenosum Balf. f.
Common Name(s): Calabar bean, Chop nut, Esere nut, Faba calabarica, Ordeal bean, Physostigma
The calabar bean is the dried ripe seed of P. venenosum, a perennial woody climbing plant found on the banks of streams in West Africa. Vines of the plant extend more than 15 m tall, climbing high among the trees. The plant bears showy purple flowers and seed pods that grow to about 15 cm in length. Each pod contains 2 to 3 seeds. The dark brown seeds are about 2.5 cm wide and thick and have an extremely hard shell.Duke 2002, USDA 2014
The plant is native to an area of Africa around Nigeria once known as Calabar, and the seeds were used as an "ordeal poison" to determine if a person was a witch or possessed by evil spirits. When used for this purpose, the victim was made to ingest several beans; if the person regurgitated the beans and survived the "ordeal," his innocence was proclaimed. Western settlers who were captured by native tribes and who underwent the "ordeal" learned not to chew the bean but to swallow it intact, thereby avoiding release of the toxic constituents. The plant has been long recognized as a commercial source of the alkaloid physostigmine, first isolated in 1864 and used experimentally to counteract the effects of atropine and for miotic effects in the eyes.Calabrese 2008, Karczmar 1998, Nickalls 1988, Proudfoot 2006, Realini 2011
The seeds contain the alkaloid physostigmine (eserine) in a concentration of about 0.15%, along with the related alkaloids eseramine, physovenine, calabatine, and geneserine, and others. These alkaloids are derived from a tryptophan precursor. Because physostigmine oxidizes to a reddish compound known as rubreserine when exposed to air, it should be protected from air and light.Zhao 2004
Uses and Pharmacology
Physostigmine alone is an acetylcholinesterase inhibitor that prolongs the neuronal activity of acetylcholine. It is used clinically to contract the pupil of the eye, often to counter the dilating effects of mydriatic drugs; to reverse the CNS toxicity of anticholinergic drugs (including tricyclic antidepressants); and to manage intraocular pressure in patients with glaucoma. It is also used in myasthenia gravis.
Cognitive function was improved in rodent studies with physostigmine.Howes 2011
Calabar bean has been widely studied as the pure alkaloid physostigmine; however, the bean is toxic and should not be used.Duke 2002
Pregnancy / Lactation
Avoid use. Documented adverse effects.Ernst 2002
None well documented.
There are few reports regarding adverse reactions, aside from acute toxicity (calabar bean is toxic to humans).
Physostigmine is extremely toxic, with an oral median lethal dose of 4.5 mg/kg in mice. Physostigmine affects heart contractility and induces respiratory paralysis, which can result in death; 2 to 3 beans are sufficient to be lethal.Duke 2002
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