Comfrey

Purported Benefits, Side Effects & More
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Comfrey

Common Names

  • Slippery root
  • Knitbone
  • Blackwort
  • Bruisewort

For Patients & Caregivers

Tell your healthcare providers about any dietary supplements you’re taking, such as herbs, vitamins, minerals, and natural or home remedies. This will help them manage your care and keep you safe.


How It Works

Although comfrey has been used historically for various conditions, cases of liver toxicity have been reported.

Comfrey leaves and roots have been used for many centuries for wound healing, inflammation, and other conditions, but these effects have not been confirmed in humans through clinical trials.

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

Purported Uses and Benefits
  • 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
    Lab studies show that comfrey leaves have wound healing effects, but human data are lacking.
Patient Warnings
  • In 2001 the FDA, 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 animal experiments suggest it can cause liver cancer.
  • Comfrey has been confused with foxglove, a poisonous plant with similar leaves. Several cases of accidental ingestion of what was thought to be comfrey herbal tea occurred, resulting in 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 historically for wound healing and other conditions. 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. Although preliminary data on topical formulations suggest it may relieve pain (14) (17) (18), 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 hepatotoxic, mutagenic, and carcinogenic (13) (24), and hepatotoxicity with oral use of comfrey has been cited in the medical literature (5) (6) (7) (8) (9) (10). In addition, misidentification with foxglove has led to several cases of accidental ingestion of what was thought to be comfrey herbal tea, resulting in cardiac glycoside poisonings (15) (22) (23).

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 and Benefits
  • Wound healing
  • Pain
  • Bronchitis
  • Peptic ulcers
  • Cancer
Mechanism of Action

Preclinical studies suggest allantoin and rosmarinic acid compounds in comfrey may be responsible for cell proliferation and anti-inflammatory effects (20). Comfrey was also shown to stimulate granulation and tissue regeneration, and support callus formation (19).

Although systemic absorption following use of topical comfrey preparations is not known, an evaluation in human skin samples suggests there may be an overestimation of risk for pyrrolizidine alkaloid absorption (25).

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, mutagenic, and carcinogenic (12) (24).
  • Comfrey has been confused with foxglove, a poisonous plant with similar leaves. 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

Case reports

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 July 8, 2022.
  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.
  24. Mei N, Guo L, Fu PP, et al. Metabolism, genotoxicity, and carcinogenicity of comfrey. J Toxicol Environ Health B Crit Rev. Oct 2010;13(7-8):509-526.
  25. Kuchta K, Schmidt M. Safety of medicinal comfrey cream preparations (Symphytum officinale s.l.): The pyrrolizidine alkaloid lycopsamine is poorly absorbed through human skin. Regul Toxicol Pharmacol. Dec 2020;118:104784.
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