# Comfrey (Symphytum officinale)

**Symphytum*, “grow together”; knitbone*

**Known today as.** *Symphytum officinale*.

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

> **Caution.** Not to be taken by mouth.

## What was it used for?

Poultices to knit broken bones and heal wounds; syrups for the lungs.

## What does modern science say?

Its allantoin helps skin heal, but its pyrrolizidine alkaloids damage the liver; it is for the skin only. A controlled trial in 2004 found a comfrey root ointment eased sprained ankles as well as a standard anti-inflammatory gel. In 2001 the United States forbade its sale for internal use after cases of veno-occlusive disease of the liver, and most countries now limit even the ointment to unbroken skin for a few weeks a year.

## Pharmacognosy and toxicology

- **allantoin**: promotes the growth of skin
- **symphytine**: a pyrrolizidine alkaloid
- **echimidine**: 
- **rosmarinic acid**: 

**Mechanism.** The alkaloids are converted in the liver to pyrroles that bind its DNA and proteins.

**Dose.** Cumulative; cases from months of the tea.

**Standing.** Internal use withdrawn in the United States, where the FDA advised makers in 2001 to pull it from supplements, and barred in Germany, which allows only external products; the ointment allowed on unbroken skin for limited periods.

## What lore surrounds it?

Its country names, knitbone and boneset, record the use: the grated root, packed around a broken limb, set hard as it dried into a cast, and the mucilage gave the belief that the bone itself was being knitted. Henry Doubleday’s Russian comfrey of the 1950s was promoted as a wonder fodder and compost plant before its alkaloids were understood.

## What did the older authorities say?

**Dioscorides.** Gives the root of *symphyton*, “the uniter,” for wounds and broken bones, and says the root is so glutinous that pieces of meat boiled with it grow together.

**Gerard.** Writes that the roots “glue together fresh wounds” and are good against ruptures and broken bones, a judgement every later herbal repeated.

## Sources

- Dioscorides, *De materia medica*.
- Koll, R., et al. (2004). “Efficacy and tolerance of a comfrey root extract in the treatment of ankle distortion.” *Phytomedicine* 11.
- Gerard, J. (1597). *The Herball*.
- Stickel, F., and Seitz, H. K. (2000). *Public Health Nutrition* 3.

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

Historical description, not medical advice.