The role of your cancer health professional is to create an environment of openness and trust, and to help in making informed decisions about alternative/ complementary therapies. Collaboration will improve the safe integration of all therapies during your experience with cancer. The "Summary" and "Professional Evaluation/ Critique" sections of this Unconventional Therpaies manual are cited directly from the medical literature, and are intended to help in the objective evaluation of alternative/complementary therapies.
Summary
"One should entirely forgo the internal administration of the drug [comfrey], due to the presence, however small, of pyrrolizidine alkaloids which have hepatotoxic and carcinogenic effects." (Physician's Desk Reference)
"In view of the hepatotoxic properties documented for the pyrrolizidine alkaloid constituents, comfrey should not be taken internally. The topical application of comfrey-containing preparations to broken skin should be avoided... Comfrey should not be taken during pregnancy or lactation." (Newall)
Description/ Source/ Components
"An oil is extracted from the leaves and roots of Symphytum officinale, a member of the Borage family (Boraginaceae). Comfrey is a perennial herb that grows in temperate regions, including western Asia, North America, and Australia." (Fetrow)
"Comfrey products are marketed as herbal teas, herb root powders, and as capsules." (Ridker 1989 Mar 25)
"Symphytum officinale (common comfrey) is a traditional European dietary and medicinal herb." (Abbott)
Comfrey or Russian Comfrey is the common name for the herb Symphytum officinale. The active ingredient is allantoin which is found in the roots and leaves. (Lucas) Comfrey is also known as blackwort or knitbone. (Mairesse)
Comfrey herb and leaf contains allantoin and rosmarinic acid. Comfrey root contains allantoin, mucopolysaccharides, and various amounts of pyrrolizidine alkaloids. (Blumenthal)
"Comfrey root contains about ten times the concentration of PAs found in the leaves... All comfrey root-containing products are no longer acceptable in Canada." (Tyler)
The pyrrolizidine alkaloids that are contained in comfrey are symphytine, symlandine, echimidine, intermidine, lycopsamine, myoscorpine, acetylcopsamine, acetylintermidine, lasiocarpine, heliosupine, viridiflorine, and echiumine. (Newall)
Allantoin is a product of purine metabolism. (Merck)
History
Comfrey has been used since the sixteenth century for wound healing, inflammation, gout, ulcers, gangrenes. It has been used in the 20th century for treating malignancies. (Lucas)
Comfrey root and leaves are also used to treat pulmonary hemorrhages, diarrhea, dysentery, internal ulcers, glandular disorders, chronic coughs, bronchitis and gout, as gargles to treat hoarseness and sore gums and as fomentation used to treat varicose veins, inflammations, burns, sores, sprains, fractures, gangrene, otitis, mastitis, fibrositis, pleurisy and bronchitis. (Mairesse)
"The plants high concentration of mucilage provides rationale for comfrey's historical usage in treating stomach ulcers, inflammatory bowel disease, and for upper respiratory conditions" (McGuffin)
Proponent/ Advocate Claims
Comfrey has been thought to be an herb with medicinal properties. Proponents have occasionally claimed its usefulness as a cancer therapy.
Professional Evaluation/ Critique
There is no evidence that comfrey inhibits cancer growth in animals or humans.
"Both leaves and roots of comfrey contain allantoin, a naturally occurring substance that promotes tissue growth." (McGuffin)
"Carcinogenicity has been described in rats fed a diet supplemented with comfrey. The mutagenicity of comfrey has been attributed to lasiocarpine, which is known to be mutagenic and carcinogenic." (Newall)
"Pyrrolizidine alkaloids, which are present in many varieties of plant but particularly those of the Senecio species, have been identified in Symphytum officinale." Studies by Hirono revealed that the pyrrolizidine alkaloids - senkirkine and symphytine - caused liver tumours in rats."
Carcinogenicity of Symphytum officinale was studied in three groups of male rats. Group l received injections of freshly prepared senkirkine. Group 2 received injections of symphytine. Group 3 received injections of a salt and water solution. Nine of the 20 rats in group 1 developed liver cell adenoma. Of 20 rats in group 2, 4 developed liver tumors, 3 developed hemangioendothelial sarcomas (malignant tumors formed by the proliferation of endothelium) and one had liver cell adenoma. The hemangioendothelial sarcomas showed metastasis in the lungs of two rats. Group 3 developed no liver tumors. (Hirono 1979)
Earlier experiments by Hirono demonstrated the development of hepatocellular adenomas in rats, which had been fed diets containing comfrey roots and leaves. (Hirono 1978)
"Canadian health authorities have already moved to ban the sale of certain comfrey products." (Ridker 1989 Dec)
Toxicity/ Risks
"The toxicity of pyrrolizidine alkaloids is well recognized... Acute toxicity results in hepatic necrosis whereas chronic toxicity typically results in veno-occlusive disease characterized by the presence of greatly enlarged liver cells." (Newall)
"Relative toxicities vary widely depending on the part of the plant consumed and from one species to another of the same genus. For example, the concentration of alkaloids in comfrey is measured at about 10 times higher in the root than in the leaf. Moreover, echimidine, the most toxic of the alkaloids found in comfrey, is present in the so-called Russian comfrey species (S. asperum and its cultivars) but is completely absent in most cytotypes of S. officinale. Except for those manufacturers of botanical supplements who use botanically referenced materials or analyze for echimidine, the toxic species is not readily excluded from trade." (McGuffin)
"Lasiocarpine (LC), a pyrrolizidine alkaloid, is able to induce a series of chronic and progressive lesions in rat liver, including a long-lasting block in the cell cycle, the appearance of enlarged hepatocytes (megalocytosis), fibrosis, cirrhosis and malignant neoplasm." (Laconi)
"The effects of pyrrolizidine alkaloids are cumulative, and overt damage may be delayed for a long time." (Winship)
"The diagnosis of veno-occlusive disease in a newborn infant who subsequently died highlights the susceptibility of the foetus to pyrrolizidine alkaloid toxicity. In this case the mother had consumed a herbal tea as an expectorant during pregnancy." (Newall)
It is known that cows, horses, and sheep can die from liver damage when grazing on plants containing hepatotoxic PA. (Winship)
"Venoocclusive disease, a form of Budd-Chiari syndrome, was diagnosed in a 49 year old woman. Analysis of food supplements the woman regularly consumed showed the presence of pyrrolizidine alkaloids. The major source was a powder purporting to contain ground comfrey root... The clinical and analytic findings were consistent with chronic pyrrolizidine intoxication, indicating that low-level, chronic exposure to such alkaloids can cause venoocclusive disease." (Ridker 1985)
A food supplement containing Symphytum is widely available in the United States. "Numerous brands of comfrey-pepsin capsules and tablets are sold in herbal and health-food stores as a digestive aid. Users take them daily over long periods or even permanently." Analysis of two brands of the capsules revealed the presence of pyrrolizidines. In the case of veno-occlusive disease reported by Ridker, it was estimated that the patient had consumed a total of 85 mg [milligrams] of alkaloids - the equivalent of nine days' use of the preparation. (Huxtable)
"Although the PA toxicity is the most significant hazard associated with the use of comfrey, it is not the only one. Several cases of atropine poisoning following the consumption of comfrey products have appeared in the literature. (Awang)
The plant that is the most likely cause of such contamination is deadly nightshade (Atropa belladonna L.), the leaves of which could be mistaken for comfrey by inexperienced collectors... Several cases of digitalis poisoning have resulted from mistaking foxglove [Digitalis purpurea L.] leaves for comfrey leaves. Such occurrences emphasize the lack of quality control in some segments of the herb industry." (Tyler)
"Products sold in health food stores are not regulated by the government in terms of either safety or efficacy, and thus are a potential health hazard. Consumption of comfrey and its teas should be avoided." (Bach)
Fetrow's list of adverse reaction to Comfrey includes carcinogenic potential (caused hepatocellular adenomas and urinary bladder tumors in animals). Hepatotoxicity: venoocclusive disease caused by pyrrolizidine alkaloids in the plant. (Fetrow)
References
Abbott PJ. Comfrey: assessing the low-dose health risk. [review]. Medical Journal of Australia 1988 Dec 5-19;149:678-682.
Awang DVC , Kindack DG. Lancet II 1989;44.
Bach N, Thung SN, Schaffner F. Comfrey herb tea-induced hepatic veno-occlusive disease. American Journal of Medicine 1989 July;87:97-99.
Blumenthal M, et al. Complete German commission E monographs - therapeutic guide to herbal medicines. Austin: American botanical council, 1998:115-116.
Fetrow CW, Avila JR. Professional's handbook of complementary and alternative medicines. Springhouse, Pennsylvania: Springhouse Corporation 1999:191-93.
Hirono I, Hideki M, Masanobu H. Carcinogenic activity of Symphytum officinale. JNCI 1978;61:865-868.
Hirono I, et al. Induction of hepatic tumors in rats by senkirkine and symphytine. JNCI 1979;63:469-471.
Huxtable RJ, Luthy J, Zweifel U. Toxicity of comfrey-pepsin preparations. N Engl J Med 1986;315:1095.
Laconi E, et al. Transplantation of normal hepatocytes modulates the development of chronic live lesions induced by a pyrrolizidine alkaloid, lasiocarpine. Carcinogenesis 1995;16.
Lucas R. A magic herb of proven value. In Nature's medicines: the folklore, romance and value of herbal remedies. West Nyak, N.Y.: Parker, 1966:61-69.
McGuffin M, et al. American herbal products association's botanical safety handbook. New York: CRC Press, 1997:111-112,149-151.
Mairesse M. Health secrets of medicinal herbs. New York: Arco, 1981:41-42.
Merck Index: an encyclopedia of chemicals, drugs and biologicals. 10th ed. Rathway, N.J.: Merck, 1983:39.
Newall AC, et al. Herbal medicines - a guide to health-care professionals. London: Pharmaceutical press, 1996:87-88.
Physician's Desk Reference. PDR for herbal medicines. Montvale, New Jersey: Medical Economics Company 1998:1164.
Ridker PM, McDermott WV. Comfrey herb tea and hepatic veno-occlusive disease. Lancet 1989 Mar 25;1(8639):657.
Ridker PM, McDermott WV. Hepatotoxicity due to comfrey herb tea. American Journal of Medicine 1989 Dec;87(6):701.
Ridker PM, et al. Hepatic venoocclusive disease associated with the consumption of pyrrolizidine-containing dietary supplements. Gastroenterology 1985;88:1050-1054.
Tyler VE, Foster S. Tyler's honest herbal: a sensible guide to the use of herbs and related remedies 4th Ed. New York: Haworth herbal press, 1999:121-124.
Winship KA. Toxicity of comfrey. Adverse Drug React & Toxicol Rev 1991;10(1):47-59.
Revised February 2000