# Rhubarb (Rheum officinale)

**Rabarbaro**

**Known today as.** The root of Chinese rhubarb, *Rheum officinale* and *R. palmatum*, long brought to Europe overland through the Levant; not the garden rhubarb stalk.

Kind: Plant  
Poisoning: The anthranoid purgatives (https://thethinkingpress.org/materia-medica/poisons/anthranoid)

## What did Canale use it for?

The principal purge for choleric and sanguine patients (ch. 4).

## What does modern science say?

Confirmed. Its anthraquinones are laxative in larger doses, while its tannins make it astringent in small ones, and it is still used.

## Pharmacognosy and toxicology

- **sennosides A and B**: dianthrone glycosides
- **rhein and emodin**: anthraquinones
- **tannins**: gallotannins, which astringe after the purge
- **oxalic acid**: in the leaf, which is the poison

**Mechanism.** The anthranoids pass unabsorbed to the colon, where bacteria free the anthrones that stimulate peristalsis and secretion eight to twelve hours later; the tannins then bind, which is why the old writers said rhubarb purged and then stayed. The medicinal root is *Rheum palmatum* from China; the garden stalk is a food, and its leaf’s oxalate has killed.

**Dose.** 0.5–2 g of root purges; chronic use darkens the colon lining (melanosis coli) and lowers potassium; the leaf at a few hundred grams gives oxalate kidney failure.

**Standing.** EMA monograph (2007, revised 2020) for short-term constipation; a WHO monograph; in the Chinese Pharmacopoeia as da huang.

## What lore surrounds it?

As its fame as a purge spread along the Silk Road from China through Persia, recorded by the Castilian ambassador Ruy González de Clavijo early in the fifteenth century, the finest rhubarb root came to cost more in Europe than cinnamon or saffron, the two benchmarks of medieval luxury.

## What did the older authorities say?

**Dioscorides.** Calls it *rha*, the root from beyond the Bosporus, a name taken from the river Rha, the Volga, along which it came.

## Sources

- Silk Road Gourmet, on rhubarb’s Silk Road history.
- EMA/HMPC (2007). *European Union herbal monograph on Rheum palmatum L. and Rheum officinale Baillon, radix* (EMEA/HMPC/189624/2007; revised 2020).
- Cao, Y.-J., et al. (2017). “Advances in bio-active constituents, pharmacology and clinical applications of rhubarb.” *Chinese Medicine* 12.

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*Rhubarb.* In *Materia Medica*, edited by B. C. P. Statema. Version 1, revised 2026-09-25. The Thinking Press. https://thethinkingpress.org/materia-medica/rhubarb

Historical description, not medical advice.