# Castor-oil plant, seeds of (Ricinus communis)

**Ricino*; *kerua*; *grano regale**

**Known today as.** *Ricinus communis*; Canale gives *mirasole* as its local name.

Kind: Plant  
Poisoning: Gastrointestinal irritants (https://thethinkingpress.org/materia-medica/poisons/gastrointestinal)  
Toxic: yes

> **Caution.** 

## What did Canale use it for?

Up to fifteen seeds, cleaned and powdered, or candied, as a vomit that also purges (ch. 5; note XXXVI).

## What does modern science say?

Dangerous. The seeds contain ricin, one of the most toxic natural substances, and two or three seeds have proved fatal; pressed castor oil, which leaves the ricin behind, is the safe laxative.

## Pharmacognosy and toxicology

- **ricin**: in the seed, not the oil
- **ricinoleic acid**: the purgative, in the oil

**Mechanism.** Ricin inactivates ribosomes; ricinoleic acid acts on the gut’s prostanoid receptors.

**Dose.** A few chewed seeds can kill; the pressed oil holds no ricin.

**Standing.** Castor oil is a licensed laxative; ricin is a scheduled chemical weapon.

## What lore surrounds it?

Grieve traces the plant to Herodotus, “who calls it Kiki, and states that it furnishes an oil much used by the Egyptians, in whose ancient tombs seeds of Ricinus are met with,” and to “the Kikajon of the Book of Jonah, rendered by the translators of the English Bible, ‘gourd.’” Albertus Magnus cultivated it in the thirteenth century; the name “Castor” was first applied in Jamaica, “where it seems to have been called ‘Agnus Castus,’” and the botanical name “is from the Latin Ricinus (a dog-tick), from the form and markings of the seed.” In the Canary Islands nursing mothers apply the fresh leaves “to increase the flow of milk.”

## What did the older authorities say?

**Herodotus.** Says the Egyptians pressed the oil of *kiki* to burn in their lamps.

## Sources

- Grieve, M. (1931). *A Modern Herbal*, “Castor Oil Plant.” botanical.com/botanical/mgmh/c/casoil32.html
- Audi, J., et al. (2005). “Ricin poisoning: a comprehensive review.” *JAMA* 294.

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*Castor-oil plant, seeds of.* In *Materia Medica*, edited by B. C. P. Statema. Version 1, revised 2026-10-01. The Thinking Press. https://thethinkingpress.org/materia-medica/castor-oil-plant-seeds-of

Historical description, not medical advice.