How It Works
Bottom Line: Comfrey is a dangerous herb and should be avoided.
Comfrey extracts come from the roots, leaves, and branches of the plant. 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. Because of its history of causing liver damage, using comfrey may not be worth the risks.
Purported Uses
**NOTE: Comfrey has not been shown to be effective for any of the following conditions. Many cases of liver toxicity have been reported after comfrey use, and the Food and Drug Administration has advised that all comfrey products be removed from the market.
- To treat bronchitis
- To treat cancer
- To reduce inflammation in conditions such as rheumatoid arthritis
- To treat peptic ulcers
- To improve wound healing
Research Evidence
No clinical trials have shown any positive effects of comfrey, but many studies have shown that it can cause liver damage.
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. (For more information, see http://www.cfsan.fda.gov/~dms/dspltr06.html).
- Comfrey contains compounds that are toxic to the liver and can cause liver cancer.
- This product is regulated by the F.D.A. as a dietary supplement. Unlike approved drugs, supplements are not required to be manufactured under specific standardized conditions. This product may not contain the labeled amount or may be contaminated. In addition, it may not have been tested for safety or effectiveness.
Side Effects
Scientific Name
Symphytum officinale
Common Name
Slippery root, knitbone, blackwort, bruisewort
Clinical Summary
Derived from the root, leaves, and branches. In June 2001, the FDA asked all manufacturers to remove products containing comfrey from the market
(12). No clinical studies support the use of oral comfrey, and there is an extensive literature concerning hepatotoxicity
(5) (6) (7) (8) (9) (10). The risk of systemic absorption following the use of topical comfrey preparations is unknown.
Purported uses
- Bronchitis
- Cancer treatment
- Inflammation
- Peptic ulcers
- Rheumatoid arthritis
- Wound healing
Constituents
- 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
(1)
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.
(4)
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. (Full text available at
http://www.cfsan.fda.gov/~dms/dspltr06.html) Comfrey contains unsaturated pyrrolizidine alkaloids, which are hepatotoxic and hepatocarcinogenic.
(2) (3) (12)
Adverse Reactions
Reported: Hepatotoxicity
Literature Summary and Critique
There are no clinical studies that document any positive effects of comfrey, but many studies have shown hepatotoxicity.
(5) (6) (7) (8) (9) (10)
References
- Newall C, et al. Herbal Medicines: A Guide for Health-Care Professionals. London: Pharmaceutical Press; 1996.
- Schulz V, et al. Rational Phytotherapy: A Physicians Guide to the Use of Herbs and Related Remedies, 3rd ed. Berlin (Germany): Springer; 1998.
- Awang DVC. Comfrey. Can Pharm J 1987;120:101-4.
- Tyler V. Herbs of Choice: The Therapeutic use of Phytomedicinals. Binghamton: Pharmaceutical Products Press; 1994.
- Ridker PN, McDermott WV. Hepatotoxicity due to comfrey herb tea. Am J Med 1989;87:701.
- Ridker PN, McDermott WV. Comfrey herb tea and hepatic veno-occlusive disease. Lancet 1989;1:657-8.
- Ridker PM, et al. Hepatic veno-occlusive disease associated with the consumption of pyrrolizidine-containing dietary supplements. Gastroenterology 1985;88:1050-4.
- Yeong ML, et al. Hepatic veno-occlusive disease associated with comfrey ingestion. J Gastroenterol Hepatol 1990;5:211-4.
- Weston CFM, et al. Veno-occlusive disease of the liver secondary to ingestion of comfrey. Br Med J 1987;295:183.
- Roitman JN. Comfrey and liver damage (letter). Lancet 1981;1:944.
- 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.
- FDA advises dietary supplement manufacturers to remove products containing comfrey from the market. Available from http://www.cfsan.fda.gov/~dms/dspltr06.html (accessed September 20, 2007).
