Comfrey

Symphytum officinale

Family: Boraginaceae Part used: Leaves, root (topical preparations only)

Key Compounds

• Allantoin
• Rosmarinic acid
• Caffeic acid
• Chlorogenic acid
• Lithospermic acid
• Symphytine
• Echimidine
• Lasiocarpine
• Mucilaginous polysaccharides
• Tannins
• Beta-sitosterol
• Pyrrolizidine alkaloids (PA)

Traditional Use

• Blunt trauma, sprains, and bruises — German Commission E approved topical comfrey preparations for these indications; the 2004 Predel et al. RCT (203 patients, ankle sprains) showed significant superiority of 10% comfrey root extract cream over diclofenac gel for pain and swelling reduction; the anti-inflammatory and cell-regeneration effects complement each other in acute soft tissue injury; allantoin reduces inflammation and stimulates repair simultaneously
• Wound healing — allantoin promotes cell proliferation by stimulating the mitotic activity of fibroblasts and epithelial cells; this accelerates surface wound closure; CRITICAL LIMITATION: this same property can cause superficial wound closure before deeper wound layers have healed, trapping infection; comfrey should only be used on clean, superficial wounds, not on puncture wounds, deep lacerations, or infected wounds
• Osteoarthritis topical — a 2004 Grube et al. RCT (220 OA knee patients, comfrey root extract gel vs placebo) showed significant reduction in pain on movement and at rest; the topical anti-inflammatory compounds (rosmarinic acid, allantoin) provide local effect without the systemic risks of oral anti-inflammatory drugs; topical use for joint pain has reasonable clinical support
• Traditional bone-setting — European traditional medicine used comfrey internally and as poultice for fractures, sprains, and internal injuries for centuries; the name 'knitbone' reflects the observed clinical effect; internal use is no longer recommended due to pyrrolizidine alkaloid hepatotoxicity; the topical evidence base is the modern successor to this tradition
• Pyrrolizidine alkaloid hepatotoxicity — pyrrolizidine alkaloids (symphytine, echimidine, lasiocarpine) are hepatotoxic compounds converted in the liver to reactive pyrroles that cause hepatic veno-occlusive disease and have shown carcinogenicity in animal studies; internal comfrey use has been associated with fatal hepatic veno-occlusive disease in humans; the US FDA issued a ban on internal comfrey products in 2001; European regulatory agencies require PA-reduced or PA-free preparations for topical use (limit: 1 mcg PA per day application)

Comfrey was called knitbone. It was used to knit bone.

Not metaphorically — the word knit here means to join, to bind together, the same root as knitting needles drawing loops together into cloth. Medieval herbalists applied the plant to fractures and observed that tissue united. The genus name Symphytum comes from Greek: sympho, I grow together. The Latin con + firmare (to make firm) gives the common name comfrey. Every name this plant has acquired — in English, Latin, and Greek — is pointing at the same thing.

The mechanism was discovered in 1912: allantoin, a compound that stimulates cell proliferation. The plant knew what it was doing.

Meet the plant

A robust perennial of temperate Europe and western Asia, growing in moist ground along streams and roadsides. Large rough-textured leaves (15–30 cm), hollow stems, drooping clusters of tubular purple-pink or white flowers. The root is thick, dark, mucilaginous when cut.

Both leaves and root contain allantoin. The root contains more — and also more of the alkaloids that cause the problem.

What allantoin does

Allantoin is a uric acid derivative found in comfrey at 0.6–0.8% in fresh leaves and up to 1.3% in roots. It promotes cell proliferation and migration in fibroblasts and epithelial cells — the cells responsible for wound closure and tissue repair. It also reduces inflammation.

This is why comfrey preparations work for sprains, bruises, and surface wounds: the cell-proliferating activity directly accelerates the biological processes of tissue repair, while the anti-inflammatory compounds (rosmarinic acid, caffeic acid, tannins) reduce swelling and pain simultaneously.

The critical limitation is the same property. If you apply comfrey to a deep or dirty wound, the surface epithelium closes faster than the underlying tissue heals. The wound looks healed. Inside, it is not. This is why German Commission E approval is specifically for blunt trauma, sprains, and bruises — not for deep wounds or puncture wounds.

The 2004 ankle sprain trial

Predel et al. enrolled 203 patients with ankle sprains (grade I and II) and compared 10% comfrey root extract cream to diclofenac gel — a standard pharmaceutical topical anti-inflammatory.

The comfrey group showed better pain reduction and greater reduction in ankle swelling over 8 days. Superior to the pharmaceutical control, not merely equal.

This is a noteworthy result. Topical comfrey for acute soft tissue trauma is not folk medicine seeking validation — it is a clinically supported intervention that outperformed a pharmaceutical comparator in a controlled trial.

The pyrrolizidine alkaloid problem

The same plant contains pyrrolizidine alkaloids: symphytine, echimidine, lasiocarpine.

These are converted in the liver to reactive dehydropyrrolizidine derivatives that alkylate DNA and proteins. The result is hepatic veno-occlusive disease — progressive damage to the small hepatic veins leading to liver failure. Animal studies show carcinogenicity at high doses. Human deaths from comfrey tea consumption are documented in the medical literature.

The US FDA issued an advisory banning internal comfrey products in 2001. European regulatory bodies require topical preparations to contain no more than 1 mcg of PAs per recommended daily application. Modern topical comfrey products use PA-reduced or PA-free extracts — specially bred cultivars or extraction methods that remove PAs while retaining allantoin and anti-inflammatory compounds.

The distinction: root has more PAs than leaves. Symphytum × uplandicum (Russian comfrey, the hybrid promoted as a health food in the 1970s) has approximately 10 times more PAs than S. officinale. Much of the hepatotoxicity literature involves Russian comfrey, not the true medicinal species. The problem is real regardless of species distinction.

Internal use of comfrey: do not.

What people actually do with it

Topical cream/gel (standard preparation): PA-reduced S. officinale root extract cream (2.5–10% comfrey root equivalent), applied 2–3 times daily to the affected area. German Commission E approved for sprains, bruises, and blunt trauma. Allow 2–3 weeks for injury treatment. Do not apply to open wounds or broken skin.

Poultice (traditional): Fresh leaves blanched and applied warm to bruised or sprained areas, wrapped in cloth. Less consistent allantoin delivery than standardised preparations, but the traditional method. Use only on unbroken skin.

Comfrey oil (topical): Dried leaves infused in carrier oil, applied to sore muscles and bruises. Traditional preparation for musculoskeletal use.

Caution on product labelling: Products specifying S. officinale with PA-free or low-PA certification are safer than unspecified ‘comfrey’ preparations. Avoid Russian comfrey (S. × uplandicum) preparations. Avoid any internal preparation.

Could you grow this yourself?

Easily — comfrey grows vigorously in most temperate gardens and is considered somewhat invasive once established. It spreads from root fragments, and even small root pieces left in the soil regenerate. For medicinal use, grow S. officinale specifically, not the faster-growing Russian comfrey hybrid.

Harvest leaves before flowering for lower PA content. Use topically and fresh.

Comfrey (コンフリー) in Japan

Comfrey arrived in Japan as a health food promotion in the 1970s. Cookbooks and health publications advocated consuming comfrey leaves as a nutritious green. This led to measurable rates of hepatic veno-occlusive disease, and the Japanese Ministry of Health issued a warning on comfrey ingestion in 1989 — one of the earlier regulatory actions on comfrey internationally, predating the US FDA’s 2001 advisory.

The market largely withdrew. Japanese awareness of comfrey now is primarily through topical preparations — コンフリー cream for bruises and sprains, following the European standard of external use only.

Things you’re probably wondering

Can the topical cream cause liver damage? Percutaneous absorption of PAs from intact skin is very low. Topical applications in clinical trials have not shown hepatotoxic effects. EU regulations require less than 1 mcg PA per daily topical application — this amount does not accumulate to hepatotoxic levels. For broken skin or large application areas, there is more caution warranted.

Is it the same as the comfrey in organic gardening? The Symphytum × uplandicum (Russian comfrey) used as a garden compost activator and liquid fertiliser is the high-PA hybrid, not the medicinal species. For topical medicinal use, S. officinale PA-reduced preparations are what the evidence supports.

Why did German Commission E approve topical use if the plant is toxic? Because topical use is demonstrably effective and the hepatotoxicity evidence applies to internal use. The risk of topical application of PA-reduced preparations to intact skin is different from drinking comfrey tea. Risk assessment distinguishes route of administration.

Botanical details

The full compound list

See Also

• Arnica — topical anti-inflammatory for bruises and sprains; complementary topical option; similarly not for internal use
• Calendula — topical wound-healing herb; safer for open wounds (unlike comfrey)
• Boswellia — oral anti-inflammatory for joint conditions; internal complement to comfrey’s topical applications

References

• Predel, H.G. et al. (2004). Efficacy of a comfrey root extract ointment in comparison to a diclofenac gel in the treatment of ankle sprains. Phytomedicine, 12(10), 707–714.
• Grube, B. et al. (2007). Efficacy of a comfrey root (Symphyti offic. radix) extract ointment in the treatment of patients with painful osteoarthritis of the knee. Phytomedicine, 14(1), 2–10.
• Stickel, F. & Seitz, H.K. (2000). The efficacy and safety of comfrey. Public Health Nutrition, 3(4A), 501–508.
• European Medicines Agency (2011). Assessment report on Symphytum officinale L.. EMA/HMPC/572844/2009.