Health Care Professional Information

Scientific Name
Symphytum officinale
Common Name

Slippery root, knitbone, blackwort, bruisewort

Clinical Summary

Comfrey is a fast-growing plant whose leaves and roots have been used for centuries to treat many ailments, especially for wound healing.
A study done in mice indicates that comfrey has antiproliferative effects (13) and the root extract is useful in relieving acute back pain (14). However, comfrey contains pyrrolizidine alkaloids that are hepatotoxic and carcinogenic (13). There is extensive literature concerning hepatotoxicity with use of comfrey (5) (6) (7) (8) (9) (10) but the risk of systemic absorption following the use of topical comfrey preparations is not known.

Comfrey was used since the 1930s for animal feed, but has been prohibited in Australia and New Zealand. In June 2001, the FDA asked all manufacturers to remove products containing comfrey from the market (12).
Comfrey herbal tea use resulted in several cases of cardiac glycoside poisoning due to misidentification with foxglove as the leaves of both plants look similar (15).

Purported Uses
  • Bronchitis
  • Cancer treatment
  • Inflammation
  • Peptic ulcers
  • Rheumatoid arthritis
  • Wound healing
  • Alkaloids (pyrrolizidine-type): Symphytine, symlandine, echimidine, intermidine, lycopsamine, myoscorpine, acetyllycopsamine, acetylintermidine, lasiocarpine, heliosupine, viridiflorine, and echiumine
  • Carbohydrates: Gums (arabinose, glucuronic acid, mannose, rhamnose, xylose), glucose, and fructose
  • Tannins (pyrocatechol-type) 2.4%
  • Triterpenes: Sitosterol and stigmasterol (phytosterols), steroidal saponins, and isobauerenol
  • Other constituents: Allantoin, caffeic acid, carotene, chlorogenic acid, choline, lithospermic acid, rosmarinic acid, and silicic acid
Mechanism of Action

The therapeutic value of comfrey is attributed to its content of allantoin, a cell proliferant, and rosmarinic acid, an anti-inflammatory agent and inhibitor of microvascular pulmonary injury.

Adverse Reactions

Reported: Hepatotoxicity (6) (7) (8) (9) (10)

Dosage (Inside MSKCC Only)
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  1. Newall C, et al. Herbal Medicines: A Guide for Health-Care Professionals. London: Pharmaceutical Press; 1996.
  2. Schulz V, et al. Rational Phytotherapy: A Physicians Guide to the Use of Herbs and Related Remedies, 3rd ed. Berlin (Germany): Springer; 1998.
  3. Awang DVC. Comfrey. Can Pharm J 1987;120:101-4.
  4. Tyler V. Herbs of Choice: The Therapeutic use of Phytomedicinals. Binghamton: Pharmaceutical Products Press; 1994.
  5. Ridker PN, McDermott WV. Hepatotoxicity due to comfrey herb tea. Am J Med 1989;87:701.
  6. Ridker PN, McDermott WV. Comfrey herb tea and hepatic veno-occlusive disease. Lancet 1989;1:657-8.
  7. Ridker PM, et al. Hepatic veno-occlusive disease associated with the consumption of pyrrolizidine-containing dietary supplements. Gastroenterology 1985;88:1050-4.
  8. Yeong ML, et al. Hepatic veno-occlusive disease associated with comfrey ingestion. J Gastroenterol Hepatol 1990;5:211-4.
  9. Weston CFM, et al. Veno-occlusive disease of the liver secondary to ingestion of comfrey. Br Med J 1987;295:183.
  10. Roitman JN. Comfrey and liver damage (letter). Lancet 1981;1:944.
  11. Foster S, et al. Tyler's Honest Herbal: A Sensible Guide to the Use of Herbs and Related Remedies, 3rd ed. Binghamton: Haworth Herbal Press; 1993.
  12. FDA advises dietary supplement manufacturers to remove products containing comfrey from the market. Available from Accessed May 12, 2011.
  13. Gomes MF, de Oliveira Massoco C, Xavier JG, Bonamin LV. Comfrey (Symphytum Officinale. L.) and Experimental Hepatic Carcinogenesis: A Short-term Carcinogenesis Model Study. Evid Based Complement Alternat Med. 2010 Jun;7(2):197-202.
  14. Giannetti BM, Staiger C, Bulitta M, Predel HG. Efficacy and safety of a Comfrey root extract ointment in the treatment of acute upper or low back pain: results of a double-blind, randomised, placebo-controlled, multi-centre trial. Br J Sports Med. 2009;44(9):637-41.
  15. Lin CC, Yang CC, Phua DH, Deng JF, Lu LH. An outbreak of foxglove leaf poisoning. J Chin Med Assoc. 2010 Feb;73(2):97-100.

Consumer Information

How It Works

Bottom Line: Comfrey has not been shown to treat or prevent cancer. Several cases of liver toxicity have been reported with its use.

Comfrey leaves and roots have been used for many centuries to treat several ailments. Comfrey contains two substances that have been found to be biologically active in laboratory tests: allantoin causes cells to increase the rate at which they divide, and rosmarinic acid reduces inflammation and prevents injury to the small blood vessels in the lungs. However, these effects have not been confirmed in humans through clinical trials.
Many cases of liver toxicity have been reported with use of comfrey.

Purported Uses
  • To treat bronchitis
    There is no scientific evidence to support this claim.
  • To treat cancer
    This claim is not backed by research.
  • To treat peptic ulcers
    There is no scientific evidence to support this.
  • To improve wound healing

Although comfrey was used in traditional medicine, this use has not been evaluated.

Research Evidence

A single study has shown that comfrey may help relieve acute back pain. But there are several reports of liver damage with its use.

Patient Warnings
  • On July 6, 2001 the U.S. Food and Drug Administration, along with the Center for Food Safety and Applied Nutrition, advised all dietary supplement manufacturers to remove products containing comfrey from the market:
  • Comfrey contains compounds that are toxic to the liver and can cause liver cancer.
Side Effects
  • Liver damage
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