Comfrey (Knitbone, Symphytum officinale)

Two mechanisms run in opposite directions, both real. Comfrey root is rich in allantoin, rosmarinic acid, mucilage and tannins; allantoin promotes cell proliferation and rosmarinic acid has anti-inflammatory activity, a plausible basis for the topical results, though the active fraction is unidentified. The pyrrolizidine alkaloids, by contrast, are not themselves toxic. Hepatic cytochrome P450 converts them into reactive esters that alkylate DNA and destroy the cells lining the sinusoids. The liver is damaged precisely because it does its job.

Most of the published research on this comes from one place. 100% of it is from Native to Europe and western Asia, naturalised across North America, Australia and New Zealand; the ointment trade is centred on Germany. Findings that no unrelated group has reproduced are weaker than the study count makes them look.

Every one of comfrey's names is an unproven medical claim frozen into language. Symphyton, consoude, consolidare, Beinwell, knitbone and bruisewort all assert that the root makes broken things whole, an idea that reaches modern packaging unbroken from Dioscorides without ever passing through a trial. Two genealogical traps follow the plant. The first is boneset, which drifted onto comfrey in English usage but properly names Eupatorium perfoliatum, an unrelated North American herb, so old texts and modern labels do not always mean the same plant. The second matters more: comfrey of commerce is not one taxon. Lawrence D. Hills and the Henry Doubleday Research Association popularised the hybrid Russian comfrey, S. x uplandicum, from the 1950s, and its Bocking cultivars carry more pyrrolizidine alkaloid, echimidine especially, than the common comfrey whose gentler reputation they inherited. The FDA's 2001 letter had to name S. officinale, S. asperum and S. x uplandicum together for exactly this reason.

Symphyton appears in Dioscorides and Pliny as a herb for wounds and for what they understood as knitting flesh, and the Greek root symphyo, to grow together, is the earliest surviving claim made for it. The plant travelled through the monastic and cottage gardens of medieval Europe under names that all restate the same promise, knitbone and bruisewort and healing herb. Its twentieth-century career was agricultural before it was pharmacological. In the 1950s Lawrence D. Hills and the Henry Doubleday Research Association promoted Russian comfrey, the hybrid S. x uplandicum, selecting the Bocking 4 and Bocking 14 cultivars and advocating the plant as fodder, compost and human food. That enthusiasm put a great deal of comfrey into a great many bodies before the alkaloid chemistry was understood, and the hybrid Hills championed turned out to be the more alkaloid-rich of the two.

1. 1st century CEDioscorides and Pliny describe symphyton as a wound herb; the Greek name, from symphyo, to grow together, carries the plant's founding claim.
2. Medieval EuropeComfrey becomes a fixture of cottage and infirmary gardens under the names knitbone, bruisewort and healing herb; the root is poulticed onto sprains and fractures.
3. 1950sLawrence D. Hills and the Henry Doubleday Research Association promote Russian comfrey (S. x uplandicum) as fodder, compost and food, selecting the Bocking 4 and Bocking 14 cultivars.
4. 1978Hirono and colleagues feed comfrey to ACI rats and produce hepatocellular adenomas and hemangioendothelial sarcomas of the liver.
5. 1992The CPMP list of herbs and herbal derivatives with serious risks effectively ends oral comfrey medicines in Europe.
6. 1993The American Herbal Products Association recommends comfrey be used externally only; the UK, Germany, Canada and Australia restrict or withdraw internal products through this period.
7. 6 July 2001The FDA writes to industry advising that dietary supplements containing comfrey (S. officinale, S. asperum and S. x uplandicum) be removed from the market; the FTC brings parallel enforcement actions.
8. 2005 to 2012Randomised placebo-controlled trials of topical comfrey report benefit in ankle sprain, knee osteoarthritis and back pain; Staiger's 2012 review synthesises them from the manufacturer's side.
9. 5 May 2015The EMA adopts its final herbal monograph: traditional use, cutaneous only, for minor sprains and bruises, capped at 0.35 micrograms alkaloid per day for at most 10 days in adults.
10. 2020Work in Regulatory Toxicology and Pharmacology shows lycopsamine is poorly absorbed through human skin, supporting the topical safety margin.

Comfrey belonged to the practical end of the European herbal, the cottage garden and the infirmary rather than the apothecary's cabinet. Dioscorides and Pliny described symphyton as a wound herb, and later English herbals kept the theme in the plant's names: knitbone, bruisewort, healing herb. The root was scraped, mashed and bound over the injury, where it sets into a firm cast as the mucilage dries. The leaves were eaten and fed to livestock, and comfrey remained a staple of British organic gardening as a compost activator.

Toxic principle

Pyrrolizidine alkaloids: symphytine, echimidine, lycopsamine, intermedine (up to 14 identified)

Dose in root tea

8 to 26 mg alkaloid per cup (Mei et al. 2010)

EMA topical limit

0.35 micrograms alkaloid per day, maximum 10 days, adults only

Injury pattern

Hepatic sinusoidal obstruction syndrome (veno-occlusive disease), potentially fatal

What follows is unfinished work on our side, not a finding about Comfrey (Knitbone, Symphytum officinale). A short entry is not a safe entry.

• Cost and market. We have not documented what it sells for or who sells it.
• Supply chain. We have not mapped where it is made.
• Who uses it. We have not documented the user groups.
• What could change. No forward-looking summary yet.
• How it compares. We have not set it against the alternatives.
• Children and teenagers. We have not checked what is known about younger people.
• What people take it for. We have not catalogued the claims made for it.