# Cantharides (Lytta vesicatoria)

*Spanish fly; *Lytta**

**Known today as.** The dried blister beetle *Lytta vesicatoria*.

Kind: Animal  
Poisoning: Cantharidin poisoning (https://thethinkingpress.org/materia-medica/poisons/cantharidin)  
Deadly: yes

> **Deadly.** Deadly by mouth.

## What was it used for?

Blistering plasters to draw out disease, and, disastrously, an aphrodisiac.

## What does modern science say?

Cantharidin raises blisters and harms the kidneys; a purified form was approved in 2023 for a viral skin infection. By mouth it erodes and bleeds the gut, brings blood into the urine, and can fail the kidneys, and fatal doses run from 10 to 60 mg. The same blistering, put to use, lifts off warts and molluscum: a 0.7 per cent solution was approved in the United States in 2023 for molluscum contagiosum in patients aged two and older.

## Pharmacognosy and toxicology

- **cantharidin**: 

**Mechanism.** Cantharidin inhibits protein phosphatases 1 and 2A, and so loosens the skin’s cells from one another: the blister.

**Dose.** Fatal by mouth at 10 to 60 mg; 1.5 to 3 g of beetles, about five, can kill.

**Standing.** A 0.7 per cent topical solution approved in the United States in 2023 for molluscum contagiosum.

## What lore surrounds it?

The blistering plaster of cantharides, Pomet says, was always kept ready compounded by the apothecaries, and the London *Emplastrum Epispasticum* of 1653 took whole cantharides; Culpeper commends it for drawing blisters in the neck for the toothache or for rheums in the eyes. The emperor Henry IV and the empress Livia are said to have used it as an aphrodisiac, in accounts Scott and colleagues could not trace to primary sources; Sade was sentenced to death for secretly giving it to women, but the sentence was never carried out.

## What did the older authorities say?

**The Marquis de Sade.** Was sentenced to death for secretly giving cantharidin to women; the sentence was never carried out.

**Dioscorides.** Gives the way of killing the beetles over the fumes of sharp vinegar and storing them, and reports that some held them to help dropsy by moving the urine, and their wings and feet to be an antidote.

**The empress Livia.** A story retold in a 2012 *Scientific American* article has her using cantharides at court; Scott and colleagues (2026) note that it cannot be traced to primary sources.

**Pierre Robiquet.** Isolated cantharidin, the blistering principle, in 1810, and found it a poison as fierce as strychnine.

## Sources

- Dioscorides, *De materia medica* II.
- Moed, L., et al. (2001). “Cantharidin revisited: a blistering defense of an ancient medicine.” *Archives of Dermatology* 137.
- Scott, K. A., et al. (2026). On the history, synthesis, and medicinal use of cantharidin, LB-100, and their analogs. *RSC Medicinal Chemistry* 17: 743–767.
- Zhang, J., et al. (2025). Cantharidin: a double-edged sword in medicine and toxicology. *Frontiers in Pharmacology* 16: 1644186.
- Pomet, P. (1712). *A Compleat History of Druggs*. London: Bonwicke et al.
- Culpeper, N. (1653). *Pharmacopoeia Londinensis: or the London Dispensatory*. London: Peter Cole. Text Creation Partnership edition A35381.
- Moed, L., et al. (2001). *Archives of Dermatology* 137.

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*Cantharides.* In *Materia Medica*, edited by B. C. P. Statema. Version 1, revised 2026-10-03. The Thinking Press. https://thethinkingpress.org/materia-medica/cantharides

Historical description, not medical advice.