By Donald J. Brown, ND
Healthnotes Newswire — Herbal products containing comfrey pose a health risk to consumers due to the presence of toxic substances that may damage the liver, according to an advisory letter the Food and Drug Administration (FDA) sent to dietary supplement industry leaders last week. 1
Addressed to such notable industry groups as the American Herbal Products Association, the American Botanical Council, and the Council for Responsible Nutrition, the letter focuses on the potentially toxic ingredients in comfrey known as pyrrolizidine alkaloids (PAs). These constituents of comfrey and other plants have been found to cause liver damage in animal experiments,2 and have been implicated in cases of liver disease in people consuming large amounts of comfrey in capsules or as a tea.3 4 5 The letter also points to evidence suggesting PAs may also be cancer-causing.6
The letter advised herbal supplement manufacturers to remove products currently on the market that may contain comfrey and to ask customers who may be using them to stop immediately. In addition to common comfrey (Symphytum officinale), the warning extends to other types of comfrey, including prickly comfrey (Symphytum asperum) and Russian comfrey (Symphytum x uplandicum). The FDA also ask manufacturers to report any adverse events that may be related to the consumption of comfrey products.
Concern about comfrey-containing and particularly PA-containing herbal supplements has been a foremost concern of the herbal products industry for many years and most manufacturers have already taken steps to remove these products from store shelves. In July 1996, the American Herbal Products Association Board of Trustees recommended that all botanical ingredients containing toxic PAs, including comfrey, display a cautionary statement that directs consumers to only use the products topically only when the skin is free of abrasions or cuts.7 They also advised that nursing women avoid all uses of these products including topical applications.
Interestingly, the FDA warning does not extend to other herbs known to contain PAs. These include coltsfoot (Tussilago farfara), borage (Borago officinalis) (concern is primarily with the whole seeds, not the seed oil), and boneset (Eupatorium perfoliatum). Consumers should avoid internal use of any herbal products that contain these herbs.
Finally, consumers should note that the young leaves and the roots of comfrey are highest in PAs.8 Mature leaves of common comfrey contain extremely low levels of PAs.
Consumers are encouraged to limit their use of comfrey to topical applications. Those inclined to use the herb internally should seek products made only from the mature leaves of common comfrey (not Russian or prickly comfrey) and from which potentially harmful PAs have been removed. Even with these precautions, some experts recommend limiting internal use to no more than four to six weeks per year.9 Pregnant and nursing women should avoid all internal use of comfrey.
References1. FDA advises dietary supplement manufacturers to remove comfrey products from the market. U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition: July 6, 2001. URL: http://www.cfsan.fda.gov/~dms/dspltr06.html
2. Newall CA, Anderson LA, Phillipson JD. Herbal Medicines: A Guide for Health-Care Professionals. London: the Pharmaceutical Press, 1996.
3. Weston CFM, Cooper BT, Davies JD, et al. Veno-occlusive disease of the liver secondary to ingestion of comfrey. Br Med J 1987;295:183.
4. Ridker PM, McDermott WV. Comfrey herb tea and hepatic veno-occlusive disease. Lancet 1989;1(8639):657–8.
5. Yeong ML, Swinburn B, Kennedy M, Nicholson G. Hepatic veno-occlusive disease associated with comfrey ingestion. J Gastroenterol Hepatol 1990;5:211–14.
6. Hirono I, Mori H, Haga M. Carcinogenic activity of Symphytum officinale. J Nat Caner Inst 1978;61:865–9.
7. McGuffin M, Hobbs C, Upton R, Goldberg A (eds). American Product Association’s Botanical Safety Handbook. Boca Raton, FL: CRC Press, 1997, 111–2.
8. Yarnell E. Botanical heptotoxicity: A critical review and update. Healthnotes Rev Comp Integrative Med 2000;7:119–24.
9. McGuffin M, Hobbs C, Upton R, Goldberg A (eds). American Product Association’s Botanical Safety Handbook. Boca Raton, FL: CRC Press, 1997, 111–2. Donald J. Brown, ND, is a naturopathic physician and one of the leading authorities in the United States on evidence-based herbal medicine. He is the founder and director of Natural Products Research Consultants, Inc., and serves on the Advisory Board of the American Botanical Council and the President's Advisory Board of Bastyr University.