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Calabar Bean

Scientific Name(s): Physostigma venenosum Balf. f.
Common Name(s): Calabar bean, Chop nut, Esere nut, Faba calabarica, Ordeal bean, Physostigma

Medically reviewed by Last updated on Sep 21, 2020.

Clinical Overview


Originally consumed in African rituals that resulted in the death of many participants, the bean produces alkaloids used clinically to contract the pupil, manage ocular pressure in glaucoma, reverse the toxicity of certain other drugs, and treat myasthenia gravis. However, because of the bean’s toxicity and lack of clinical trials using the crude plant material or extract, potential uses cannot be supported or recommended.


Calabar bean’s constituent physostigmine has been widely studied as the pure alkaloid. Clinical data relating to the crude plant material or to an extract are lacking.


Contraindications have not yet been identified.


Avoid use. Documented adverse effects.


None well documented.

Adverse Reactions

There are few reports regarding adverse reactions, aside from acute toxicity (calabar bean is toxic to humans).


Calabar bean contains physostigmine, which is extremely toxic. It affects heart contractibility and induces respiratory paralysis, which can result in death.

Scientific Family

  • Fabaceae (pea/bean)


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.


Animal data

Cognitive function was improved in rodent studies with physostigmine.Howes 2011

Clinical data

Physostigmine from the calabar bean has been investigated for its ability to increase cognition, particularly in patients with Alzheimer disease, but with minimal success.Howes 2011, Howes 2012


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.

Adverse Reactions

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


Calabrese EJ. Alzheimer's disease drugs: an application of the hormetic dose-response model. Crit Rev Toxicol. 2008;38(5):419-451.18568864
Duke JA. Handbook of Medicinal Herbs. 2nd ed. Boca Raton, FL: CRC Press; 2002.
Ernst E. Herbal medicinal products during pregnancy: are they safe? BJOG. 2002;109(3):227-235.11950176
Howes MJ, Houghton PJ. Ethnobotanical treatment strategies against Alzheimer’s disease. Curr Alzheimer Res. 2012;9(1):67-85.22329652
Howes MJ, Perry E. The role of phytochemicals in the treatment and prevention of dementia. Drugs Aging. 2011;28(6):439-468.21639405
Karczmar A. Invited review: Anticholinesterases: dramatic aspects of their use and misuse. Neurochem Int. 1998;32(5-6):401-411.9676738
Nickalls RW, Nickalls EA. The first use of physostigmine in the treatment of atropine poisoning. A translation of Kleinwachter's paper entitled 'Observations on the effect of calabar bean extract as an antidote to atropine poisoning'. Anaesthesia. 1988;43(9):776-779.3052162
Realini T. A history of glaucoma pharmacology. Optom Vis Sci. 2011;88(1):36-38.21131876
Physostigmine venenosum Balf. Calabar bean. USDA, NRCS. 2014. The PLANTS database (, 17 September 2014). National Plant Data Center, Greensboro, NC 27401-4901 USA.
Proudfoot A. The early toxicology of physostigmine: a tale of beans, great men and egos. Toxicol Rev. 2006;25(2):99-138.16958557
Zhao B, Moochhala SM, Tham SY. Biologically active components of Physostigma venenosum. J Chromatogr B Analyt Technol Biomed Life Sci. 2004;812(1-2):183-192.15556497


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