Boraginaceae
Symphytum officinale
Comfrey · Knitbone · Boneset
- Part used
- rootleaf
- Native range
- Europe and western Asia, widely naturalised
- Morphology
- Coarse perennial to a metre, with bristly lance-shaped leaves running down the stem and drooping clusters of purple to cream bell flowers.
What is in it
Evidence
Topical comfrey preparations have reasonable trial support for pain in sprains, strains and osteoarthritis of the knee, and are licensed for external use in several countries. That evidence does not extend to internal use, which is the dangerous one.
Safety
Contains hepatotoxic pyrrolizidine alkaloids, which cause cumulative liver damage including hepatic veno-occlusive disease. Toxicity is dose-dependent and cumulative, so a long history of use without apparent harm is not reassurance. Root concentrations are far higher than leaf. Deaths from internal use are documented, including in a child. Not for use in pregnancy or breastfeeding by any route, and not on broken skin, through which absorption rises.
Interactions: Additive liver risk with other hepatotoxic drugs and supplements
Regulatory: Internal use banned or restricted in Australia, the UK, Germany and the US. Topical products are permitted in several jurisdictions with limits on alkaloid content and duration.
How the traditions classify it
Three systems, rating the same plant. Where they disagree, none of them is correcting the others — they are separate frameworks that arrived at their categories independently.
Historical use
One of the most consistently used wound and fracture herbs in European practice, applied as a poultice to sprains, bruises and broken bones from the classical period onward. The common names knitbone and boneset record the claim.
Recorded as history and attributed where possible. Long use establishes that a plant was widely used, not that it worked, and not that it was safe.
Worth knowing
Comfrey is the cleanest example in this collection of a plant that is genuinely useful and genuinely dangerous by the same route — the difference being which side of the skin it is on.
It is also the best illustration of why cumulative toxins defeat traditional evaluation. A tradition can spot a plant that makes people sick within hours. It cannot spot one that damages livers over years, because nothing in the experience of using it connects the dose to the outcome.
Nomenclature verified against GBIF backbone taxonomy.