Comfrey

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Comfrey

Common Names

  • Slippery root
  • Knitbone
  • Blackwort
  • Bruisewort

For Patients & Caregivers

How It Works

Comfrey has not been shown to treat or prevent cancer. Cases of liver toxicity have been reported with its use.

Comfrey leaves and roots have been used for many centuries to treat several ailments, but studies are very limited. 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. Other lab experiments suggest wound healing with a topical formula. However, these effects have not been confirmed in humans through clinical trials. 

Many cases of liver toxicity have been reported with use of comfrey. Comfrey has also been confused with foxglove, a poisonous plant, which has resulted in several cases of accidental poisoning.

Purported Uses
  • To treat bronchitis
    There is no scientific evidence to support this claim.
  • To treat pain
    A review of herbal medicine for low back pain did not find sufficient evidence for topical use of comfrey.
  • 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
    Laboratory studies show that comfrey leaves have wound healing effects. Human data are lacking.
Patient Warnings
  • In 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.
  • Comfrey has been confused with foxglove, a poisonous plant, which has similar leaves. Consequently, several cases of accidental ingestion of what was thought to be comfrey herbal tea occurred, resulting in accidental poisoning and death in one case.
Side Effects

Liver damage

 

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For Healthcare Professionals

Scientific Name
Symphytum officinale
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. Preclinical studies suggest that oral comfrey has antiproliferative effects (13), and a topical formulation showed wound healing properties (16).

Studies in humans are very limited. Topical formulations of comfrey root extract may relieve acute back pain (14) (17) and knee osteoarthritis (18), but a Cochrane Review of herbal medicine for low back pain did not find sufficient evidence for its use (21).

Comfrey contains pyrrolizidine alkaloids that are both hepatotoxic and carcinogenic (13), and there is extensive literature concerning hepatotoxicity with use of oral comfrey (5) (6) (7) (8) (9) (10). In addition, several cases of ingestion of what was thought to be comfrey herbal tea resulted in cardiac glycoside poisoning due to misidentification with foxglove as the leaves of both plants look similar (15) (22) (23). 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)

Purported Uses
  • Wound healing
  • Pain
  • Bronchitis
  • Cancer 
  • Peptic ulcers
Mechanism of Action

The mechanism of action has not been elucidated, but the therapeutic properties of comfrey are thought to be based on its anti-inflammatory and analgesic properties. Comfrey was shown to stimulate granulation and tissue regeneration, and support callus formation (18). Allantoin and rosmarinic acid, two important components, are believed responsible for cell proliferation and anti-inflammatory effects (20).

Warnings
  • In 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 (12).
  • Comfrey contains unsaturated pyrrolizidine alkaloids, which are hepatotoxic and hepatocarcinogenic (12).
  • Comfrey has been confused with foxglove, a poisonous plant, which has similar leaves. Consequently, several cases of accidental ingestion of what was thought to be comfrey herbal tea occurred, resulting in cardiac glycoside poisoning and death in one case  (15) (22) (23).
Adverse Reactions

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

References
  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 https://www.fda.gov/food/guidance-documents-regulatory-information-topic-food-and-dietary-supplements/dietary-supplements-guidance-documents-regulatory-information. Accessed February 12, 2020.
  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.
  16. Araújo LU, Reis PG, Barbosa LC, et al. In vivo wound healing effects of Symphytum officinale L. leaves extract in different topical formulations. Pharmazie. 2012 Apr;67(4):355-60.
  17. Pabst H, Schaefer A, Staiger C, Junker-Samek M, Predel HG. Combination of comfrey root extract plus methyl nicotinate in patients with conditions of acute upper or low back pain: a multicentre randomised controlled trial. Phytother Res. 2013 Jun;27(6):811-7.
  18. Laslett LL, Quinn SJ, Darian-Smith E, et al. Treatment with 4Jointz reduces knee pain over 12 weeks of treatment in patients with clinical knee osteoarthritis: a randomised controlled trial. Osteoarthritis Cartilage. 2012 Nov;20(11):1209-16.
  19. Staiger C. Comfrey: a clinical overview. Phytother Res. 2012 Oct;26(10):1441-8.
  20. Andres P, Brenneisen R, Clerc JT. Relating antiphlogistic efficacy of dermatics containing extracts of Symphytum officinale to chemical profiles. Planta Med. 1989;55:66–67.
  21. Gagnier JJ, Oltean H, van Tulder MW, et al. Herbal Medicine for Low Back Pain: A Cochrane Review. Spine (Phila Pa 1976). Jan 2016;41(2):116-133.
  22. Vithayathil MK, Edwards M. Comfrey herbal remedy causing second-degree heart block: do not be outfoxed by digitalis. BMJ Case Rep. Dec 1 2016;2016.
  23. Wu IL, Yu JH, Lin CC, et al. Fatal cardiac glycoside poisoning due to mistaking foxglove for comfrey. Clin Toxicol (Phila). Aug 2017;55(7):670-673.
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