Comfrey Benefits

Comfrey (Symphytum officinale, family Boraginaceae) is the clearest example on this whole site of a herb that genuinely works one way and genuinely harms another. Rubbed on the skin as a standardized commercial ointment, it has been through more than half a dozen randomised controlled trials for ankle sprains, muscle pain, back pain and knee osteoarthritis — several of them head-to-head against diclofenac gel — and it held its own. Swallowed, in any form, it can destroy the small veins inside your liver. That is not a theoretical risk from a cautious regulator: it is a documented cause of death, including in a 23-year-old man who took comfrey leaves and died of liver failure, and in people whose only exposure was comfrey tea.

⚠ The rule that governs every page in this section: comfrey is a herb to rub on, never to swallow. Its pyrrolizidine alkaloids — echimidine, symphytine, lycopsamine, intermedine and their acetylated relatives — are converted by the liver into reactive molecules that attack the lining of the hepatic venules and cause hepatic veno-occlusive disease (sinusoidal obstruction syndrome). The damage is often irreversible. Oral comfrey has been removed from the market or restricted in the United States, the United Kingdom, Germany, Canada and Australia. Because those same alkaloids cross broken skin, even topical use belongs on intact skin only, for a short course, never in pregnancy or breastfeeding, and not on children.

The old country name for this plant is knitbone, and the name records the tradition honestly: comfrey was the poultice you bound over a sprain, a bruise or a fracture. What modern trials show is narrower than the folklore — comfrey relieves pain and swelling in the soft tissue around an injury; it has never been shown to make a broken bone fuse faster. But that narrower claim is real, measured, and better supported than almost any other topical herb.

Table of Contents

1. Deep-Dive Articles
2. The Product Matters as Much as the Plant
3. Where the Evidence Is Strong — and Where It Is Not
4. What Is Actually in Comfrey
5. The Hard Line: Internal Use
6. Using It Safely on the Skin
7. Key Research Papers
8. External Resources
9. Connections

Deep-Dive Articles

Four articles cover comfrey properly. If you read only one, read the fourth — it is the one that keeps people out of a hepatology clinic.

The Product Matters as Much as the Plant

Almost everything useful ever measured about comfrey was measured on one of two specific German products. If you understand which one a study used, you can read the literature; if you do not, the trials look contradictory when they are not. They differ in the part of the plant used, the species, and the alkaloid content.

Two practical consequences follow. First, a jar of home-made comfrey salve made from dug-up root is not the product in these trials; it has an unknown extract strength and an unknown alkaloid content, and the root is the alkaloid-rich part. Second, when a label says only “comfrey cream,” you cannot tell which of these two very different things you are holding. Look for the plant part, the species, the extract ratio, and an explicit statement about pyrrolizidine alkaloid content.

Outside Germany, availability is uneven. In the United States comfrey creams are sold as cosmetics rather than as licensed medicines, so the trial products are often not the ones on the shelf; in the United Kingdom and the EU, comfrey root preparations for external use fall under traditional herbal registration with a defined maximum duration of use. Prices are modest — a tube typically costs about the same as a branded diclofenac gel — so cost is rarely the deciding factor. Quality disclosure is.

Where the Evidence Is Strong — and Where It Is Not

The single most important caveat runs through the top half of that table: most of these trials were sponsored by the companies that make the products. That does not make the results false — the trials were randomised, several were double-blind, and one was independently appraised by Cochrane — but industry-funded trials report larger effects on average than independent ones, so read every number here as an optimistic estimate. An independent scoping review of comfrey’s external uses reached exactly that conclusion: promising, and in need of research that the manufacturers did not pay for.

What Is Actually in Comfrey

• Allantoin — the compound that best explains comfrey’s reputation. It is a genuine promoter of cell proliferation and desquamation (shedding of dead surface cells), and purified allantoin is a standard, unglamorous ingredient in mainstream dermatology, in everything from nappy-rash creams to after-sun lotions. It is water-soluble and not toxic. Comfrey root is one of the richest natural sources.
• Rosmarinic acid and related phenolic acids — caffeic, chlorogenic, p-coumaric and p-hydroxybenzoic acids have all been quantified in root extract by HPLC. These carry the antioxidant and anti-inflammatory activity.
• Mucilage — slippery polysaccharides that give the old name “slippery root.” They form a soft, moisture-holding film on skin. Interestingly, when researchers stripped the mucilage out of a root extract, the remaining fraction was the more strongly anti-inflammatory one in cell experiments.
• Tannins — astringent polyphenols; one American knee-osteoarthritis trial deliberately blended comfrey root extract with tannic acid.
• ⚠ Pyrrolizidine alkaloids — the hepatotoxic fraction. Comfrey has been reported to contain as many as fourteen, including 7-acetylintermedine, 7-acetyllycopsamine, echimidine, intermedine, lycopsamine, symlandine, symphytine and symviridine. They occur largely as N-oxides, which matters more than it sounds: N-oxides are converted back to the free alkaloids in the gut and are easy to under-measure in the laboratory unless a reduction step is included. The root contains substantially more than the leaf.

Mechanistically, the most satisfying modern result is that a hydroalcoholic comfrey root extract blocks NF-κB signalling at two separate points in human endothelial cells — it dampens IKK1/2 activation and IκBα degradation, and it also interferes with the p65 subunit’s movement into the nucleus. NF-κB is the master switch for inflammatory gene expression, so this gives a coherent, testable reason why a comfrey ointment reduces swelling and tenderness. It is cell-culture work, not a human study, but it is the kind of mechanism that a topical anti-inflammatory should have.

The Hard Line: Internal Use

⚠ Do not drink comfrey tea. Do not take comfrey capsules, tinctures, powders or “green drinks.” Do not eat the leaves as a vegetable, however often you see it recommended in permaculture and foraging circles.

The mechanism is well characterised. Liver enzymes oxidise pyrrolizidine alkaloids into highly reactive dehydropyrrolizidine intermediates, which bind DNA and protein in the sinusoidal endothelial cells lining the smallest hepatic veins. Those cells die, the venules obstruct, blood backs up, and the result is hepatic veno-occlusive disease: an enlarged tender liver, ascites, portal hypertension, and in severe cases liver failure. The published human cases include a 49-year-old woman who had consumed a minimum of 85 mg of pyrrolizidine alkaloids over six months from a ground comfrey root supplement, a man who died at 23 after eating comfrey leaves, and a case attributed specifically to comfrey herb tea. The same alkaloids are genotoxic and carcinogenic in rodents.

Regulators acted on this. Oral comfrey products were withdrawn or removed from sale in the United States, the United Kingdom, Germany, Canada and Australia. When five national authorities independently pull the internal use of a herb while explicitly leaving the external use available, they are telling you something specific about where the danger lies.

The fourth deep-dive article covers this in full, including what symptoms to watch for and what to do if you have been taking comfrey internally.

Using It Safely on the Skin

1. Intact skin only. Pyrrolizidine alkaloids are absorbed through skin — that has been measured directly in animals — and broken skin removes the main barrier. No open wounds, no ulcers, no weeping eczema, no mucous membranes.
2. Keep the course short. The European herbal monograph for comfrey root preparations limits self-treatment to about 10 days; German dosing rules additionally cap total external use at roughly four to six weeks per year. Treat an injury, then stop.
3. Not in pregnancy or breastfeeding. Pyrrolizidine alkaloids cross the placenta and appear in milk. No exceptions, topical included.
4. Not on children — certainly not on infants, and follow the label’s age limit for older children. Smaller bodies, developing livers, and a much higher surface-area-to-weight ratio all work against them.
5. Avoid if you have liver disease of any kind, or are on medication that already burdens the liver.
6. Buy a product that discloses its alkaloid status, and wash your hands after applying.

Key Research Papers

Every PubMed identifier below was checked live against NCBI E-utilities before it was printed — title, first author, journal and year all had to match. Where a paper could not be confirmed that way, the entry carries a PubMed topic search instead of a number that might point at the wrong article.

Ankle sprain and acute soft-tissue injury

1. Koll R, Buhr M, Dieter R, et al. Efficacy and tolerance of a comfrey root extract (Extr. Rad. Symphyti) in the treatment of ankle distorsions: results of a multicenter, randomized, placebo-controlled, double-blind study. Phytomedicine. 2004;11(6):470–477. — 142 patients, comfrey root ointment four times daily for 8 days; superior to placebo for pain (p<0.0001) and ankle oedema (p=0.0001).
2. Predel HG, Giannetti B, Koll R, Bulitta M, Staiger C. Efficacy of a comfrey root extract ointment in comparison to a diclofenac gel in the treatment of ankle distortions. Phytomedicine. 2005;12(10):707–714. — 164 patients, 82 per arm, 7 days; comfrey was confirmed non-inferior to diclofenac gel.
3. D’Anchise R, Bulitta M, Giannetti B. Comfrey extract ointment in comparison to diclofenac gel in the treatment of acute unilateral ankle sprains (distortions). Arzneimittelforschung. 2007;57(11):712–716. — A pre-specified superiority re-analysis of the same 164-patient dataset; read it as one trial, not two.
4. Kucera M, Barna M, Horáček O, Kováriková J, Kucera A. Efficacy and safety of topically applied Symphytum herb extract cream in the treatment of ankle distortion. Wiener Medizinische Wochenschrift. 2004;154(21–22):498–507. — 203 patients; a 10 % comfrey herb cream beat a 1 % version of itself, a dose-response design rather than a placebo comparison.

Muscle pain, back pain and osteoarthritis

1. Kucera M, Barna M, Horàcek O, Kàlal J, Kucera A, Hladìkova M. Topical Symphytum herb concentrate cream against myalgia: a randomized controlled double-blind clinical study. Advances in Therapy. 2005;22(6):681–692. — 215 patients with upper and lower back pain; number needed to treat 3.2.
2. Giannetti BM, Staiger C, Bulitta M, Predel HG. Efficacy and safety of comfrey root extract ointment in the treatment of acute upper or lower back pain. British Journal of Sports Medicine. 2010;44(9):637–641. — 120 patients, 4 g three times daily for 5 days; median pain on standardised movement fell 95.2 % versus 37.8 % on placebo.
3. Grube B, Grünwald J, Krug L, Staiger C. Efficacy of a comfrey root (Symphyti offic. radix) extract ointment in the treatment of patients with painful osteoarthritis of the knee. Phytomedicine. 2007;14(1):2–10. — 220 patients, 6 g of ointment daily for 3 weeks; VAS fell 51.6 mm versus 10.1 mm on placebo.
4. Cameron M, Chrubasik S. Topical herbal therapies for treating osteoarthritis. Cochrane Database of Systematic Reviews. 2013;(5):CD010538. — The independent appraisal: moderate-quality evidence that comfrey extract gel probably improves pain, with adverse events no higher than placebo.
5. Smith DB, Jacobson BH. Effect of a blend of comfrey root extract (Symphytum officinale L.) and tannic acid creams in the treatment of osteoarthritis of the knee. Journal of Chiropractic Medicine. 2011;10(3):147–156. — Small (43 participants), 6 weeks, 10 % and 20 % creams both beat the reference cream.

Wound healing, allantoin and mechanism

1. Barna M, Kucera A, Hladícova M, Kucera M. Wound healing effects of a Symphytum herb extract cream (Symphytum × uplandicum Nyman). Wiener Medizinische Wochenschrift. 2007;157(21–22):569–574. — 278 patients with fresh abrasions; complete healing in 4.08 days versus 7.05 days for the low-dose reference.
2. Seigner J, Junker-Samek M, Plaza A, et al. A Symphytum officinale root extract exerts anti-inflammatory properties by affecting two distinct steps of NF-κB signaling. Frontiers in Pharmacology. 2019;10:289. — Human endothelial cells; the clearest mechanistic account available.
3. Sowa I, Paduch R, Strzemski M, et al. Proliferative and antioxidant activity of Symphytum officinale root extract. Natural Product Research. 2018;32(5):605–609. — Quantifies allantoin and five phenolic acids; stimulates human skin fibroblasts in culture.
4. Savić VLj, Nikolić VD, Arsić IA, et al. Comparative study of the biological activity of allantoin and aqueous extract of the comfrey root. Phytotherapy Research. 2015;29(8):1117–1122. — Separates what allantoin does from what the whole extract does.
5. Araújo LU, Grabe-Guimarães A, Mosqueira VCF, Carneiro CM, Silva-Barcellos NM. Profile of wound healing process induced by allantoin. Acta Cirúrgica Brasileira. 2010;25(5):460–466. — Animal work on allantoin as an isolated compound.

⚠ Pyrrolizidine alkaloids and liver injury

1. Ridker PM, Ohkuma S, McDermott WV, Trey C, Huxtable RJ. Hepatic venocclusive disease associated with the consumption of pyrrolizidine-containing dietary supplements. Gastroenterology. 1985;88(4):1050–1054. — A 49-year-old woman; at least 85 mg of alkaloids over six months from ground comfrey root.
2. Yeong ML, Swinburn B, Kennedy M, Nicholson G. Hepatic veno-occlusive disease associated with comfrey ingestion. Journal of Gastroenterology and Hepatology. 1990;5(2):211–214. — A 23-year-old man who died of liver failure after taking comfrey leaves.
3. Bach N, Thung SN, Schaffner F. Comfrey herb tea-induced hepatic veno-occlusive disease. American Journal of Medicine. 1989;87(1):97–99. — The tea case.
4. Weston CF, Cooper BT, Davies JD, Levine DF. Veno-occlusive disease of the liver secondary to ingestion of comfrey. British Medical Journal (Clinical Research Ed.). 1987;295(6591):183.
5. Mei N, Guo L, Fu PP, Fuscoe JC, Luan Y, Chen T. Metabolism, genotoxicity, and carcinogenicity of comfrey. Journal of Toxicology and Environmental Health, Part B. 2010;13(7–8):509–526. — From the US FDA’s National Center for Toxicological Research; lists the fourteen alkaloids.
6. Brauchli J, Lüthy J, Zweifel U, Schlatter C. Pyrrolizidine alkaloids from Symphytum officinale L. and their percutaneous absorption in rats. Experientia. 1982;38(9):1085–1087. — The study that shows skin absorption is real but far smaller than oral absorption.
7. Oberlies NH, Kim NC, Brine DR, et al. Analysis of herbal teas made from the leaves of comfrey (Symphytum officinale). Public Health Nutrition. 2004;7(7):919–924. — Why alkaloid levels in tea are routinely underestimated.

Reviews and regulatory context

1. Frost R, MacPherson H, O’Meara S. A critical scoping review of external uses of comfrey (Symphytum spp.). Complementary Therapies in Medicine. 2013;21(6):724–745. — The independent review; promising, with the funding and methodology problems named plainly.
2. Staiger C. Comfrey: a clinical overview. Phytotherapy Research. 2012;26(10):1441–1448. — Useful but written by an author affiliated with the manufacturer; read it alongside Frost.
3. Rode D. Comfrey toxicity revisited. Trends in Pharmacological Sciences. 2002;23(11):497–499.
4. Schrenk D, Gao L, Lin G, et al. Pyrrolizidine alkaloids in food and phytomedicine: occurrence, exposure, toxicity, mechanisms, and risk assessment. Food and Chemical Toxicology. 2020;136:111107.
5. Salehi B, Sharopov F, Boyunegmez Tumer T, et al. Symphytum species: a comprehensive review on chemical composition, food applications and phytopharmacology. Molecules. 2019;24(12).
6. Stickel F, Seitz HK. The efficacy and safety of comfrey. Public Health Nutrition. 2000. This paper could not be confirmed by an automated identifier check, so it is given as a PubMed search rather than a numbered link.

Live PubMed Searches

1. Symphytum officinale
2. Comfrey ointment randomised trials
3. Comfrey and ankle sprain
4. Comfrey and knee osteoarthritis
5. Allantoin and wound healing
6. Pyrrolizidine alkaloid hepatotoxicity
7. Herbal hepatic veno-occlusive disease
8. Comfrey percutaneous absorption

External Resources

• LiverTox — NIH database of drug and herbal liver injury
• NCCIH — Comfrey
• European Medicines Agency — Symphyti radix herbal monograph
• PubChem — allantoin compound record
• PubChem — symphytine compound record
• World Flora Online — Symphytum officinale L. taxonomy

Connections

• All Herbs
• Comfrey — the main topic page
• Topical Use for Sprains and Bruises
• Osteoarthritis and Back Pain
• Wound Healing and Allantoin
• ⚠ Never Take It Internally
• Butterbur — the other pyrrolizidine-alkaloid herb
• Marshmallow Root — a mucilage herb that is safe internally
• Calendula — the wound herb comfrey is not
• Orthopedics — sprains, strains and joint injury

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