# Houndstongue (Cynoglossum officinale)

**Cynoglossum*, “dog’s tongue”*

**Known today as.** *Cynoglossum officinale*. A coarse, grey-leaved biennial of waste ground, named for its long, tongue-shaped, softly hairy leaves.

Kind: Plant  
Poisoning: Pyrrolizidine alkaloids (veno-occlusive disease) (https://thethinkingpress.org/materia-medica/poisons/pyrrolizidine)  
Toxic: yes

> **Caution.** Toxic to the liver.

## What was it used for?

Applied as a poultice for wounds, burns, and dog bites, and taken for coughs, in the older European herbals.

## What does modern science say?

The plant contains pyrrolizidine alkaloids that damage the liver, and it has no place in modern medicine.

## Pharmacognosy and toxicology

- **heliosupine**: a pyrrolizidine alkaloid, up to 1.5 per cent
- **echinatine**: 
- **allantoin**: 
- **tannins**: 

**Mechanism.** Externally the allantoin and tannins soothe and tighten; internally the pyrrolizidine alkaloids are among the most concentrated in any European herb and are converted in the liver to pyrroles that block the hepatic veins and alkylate DNA. It kills horses and cattle that eat it in hay.

**Dose.** No safe internal dose; the alkaloid load is above comfrey’s.

**Standing.** Internal use is warned against across Europe, where regulators restrict pyrrolizidine alkaloids in herbal products; the plant is a noxious weed in the American West.

## What lore surrounds it?

A textbook case of the doctrine of signatures: Giambattista della Porta pictured its leaves beside a dog’s head to argue that the likeness itself showed the plant’s power over the harm of dogs, the principle he stated as “that to which a sign belongs, to it also the effect belongs.”

## What did the older authorities say?

**Pliny.** The cynoglossos is the plant “the leaf of which resembles a dog's tongue, and which produces so pleasing an effect in ornamental gardening.” Pliny reports a fever cure keyed to the plant's form: “The root, it is said, of the kind which bears three stems surmounted with seed, is very useful, taken in water, for tertian, and of that with four stems, for quartan, fevers.” A similar plant bearing small burrs has a root, taken in water, “curative of wounds inflicted by frogs or serpents.”

## Sources

- Wellcome Collection, doctrine of signatures illustration (della Porta, *Phytognomonica*).
- Pliny the Elder, *Natural History* 25.41, trans. J. Bostock & H. T. Riley (1855), Perseus Digital Library.
- Roeder, E. (1995). “Medicinal plants in Europe containing pyrrolizidine alkaloids.” *Pharmazie* 50.
- Stegelmeier, B. L., et al. (1999). “Pyrrolizidine alkaloid plants, metabolism and toxicity.” *Journal of Natural Toxins* 8.

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

Historical description, not medical advice.