# Pennyroyal (Mentha pulegium)

**Pulegio**

**Known today as.** *Mentha pulegium*.

Kind: Plant  
Poisoning: Hepatotoxic monoterpenes (pulegone) (https://thethinkingpress.org/materia-medica/poisons/hepatotoxic-terpenes)  
Toxic: yes

> **Caution.** 

## What did Canale use it for?

In the bath for cold complexions (ch. 7).

## What does modern science say?

Its oil is highly toxic to the liver and has killed people taking it as an abortifacient. The oil is about four-fifths pulegone, which the liver turns into menthofuran, a poison to itself: ten millilitres has caused liver failure, and women taking it to end pregnancies have died. The herb in a tea is far weaker, but carries the same risk in quantity.

## Pharmacognosy and toxicology

- **pulegone**: 80–90 per cent of the oil
- **menthofuran**: its toxic metabolite

**Mechanism.** Menthofuran destroys the liver cell by binding its proteins.

**Dose.** 10 ml of the oil has caused liver failure; the tea is far weaker.

**Standing.** Sold as a supplement in the United States with no approved use; poison centres and the herbal references warn against it in pregnancy.

## What lore surrounds it?

The Romans cooked with it, and Apicius calls for it often; colonists in Virginia strewed it against insects, and in 1665 the Royal Society’s *Philosophical Transactions* carried a report from Virginia of a wild “pennyroyal” (the American dittany) whose bruised leaves, held to a rattlesnake’s face, were said to kill it. Its old English name, pudding grass, is from its place in the black pudding.

## What did the older authorities say?

**Pliny.** Praises *pulegium* for driving away fleas, whence its Latin name, from *pulex*, the flea, and gives it to bring on the menses and to expel the dead child.

**Aristophanes.** In *Peace* (421 BC) a character is offered pennyroyal as a contraceptive, one of the oldest such references in literature.

## Sources

- Grieve, M. *A Modern Herbal*, “Pennyroyal.” As published on botanical.com.
- Pliny, *Natural History* XX.
- Anderson, I. B., et al. (1996). “Pennyroyal toxicity.” *Annals of Internal Medicine* 124.
- Anderson, I. B., et al. (1996). *Annals of Internal Medicine* 124.

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*Pennyroyal.* In *Materia Medica*, edited by B. C. P. Statema. Version 1, revised 2026-10-01. The Thinking Press. https://thethinkingpress.org/materia-medica/pennyroyal

Historical description, not medical advice.