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Other common name(s): blackwort, bruisewort, common comfrey, knitbone, slippery root

Scientific/medical name(s): Symphytum officinale


Comfrey is a fast-growing herb native to Europe and temperate parts of Asia. It now grows in North America as well. The roots and leaves are used in herbal remedies.


Although comfrey has been used in folk medicine for many years to help heal wounds, sprains, and fractures, there have been no studies in humans to prove that it is useful. Available scientific evidence does not support the idea that comfrey is effective in treating cancer. It is not considered safe for internal use due to toxic effects on the liver. There are several varieties of comfrey, some of which contain more toxic compounds than others.

How is it promoted for use?

Comfrey has been promoted mainly to speed the healing of wounds, sprains, bruises, and bone fractures and to reduce inflammation and swelling related to these injuries.

Comfrey has also been used to treat a number of other ailments, including ulcers, gallstones, arthritis, diarrhea, colitis, cough, pleurisy, and pneumonia. A mouthwash made from comfrey is sometimes used for gum disease, hoarseness, and sore throat. Some proponents also claim comfrey has anti-cancer properties.

What does it involve?

Ointments, salves, and creams that contain comfrey are available for external use. Compresses and poultices are made from the crushed roots and leaves of comfrey or from liquid extracts pressed out of the plant. They are placed directly on bruises, wounds, or sprains, are covered with a dressing, and are replaced daily until healing occurs. For internal use, dried comfrey root or leaves are sometimes prepared as a tea.

In 2001, the U.S. Food and Drug Administration (FDA) asked manufacturers of dietary supplements to remove products containing comfrey from the market because of its potential to cause liver damage. However, whole leaves and roots and extracts of both are still available. Most comfrey capsules now contain whole-leaf comfrey. Comfrey can also be purchased to grow at home.

Comfrey has been approved by Commission E (Germany's regulatory agency for herbs) to be sold only in preparations that supply no more than 100 micrograms per day if applied to the skin and no more than 1 microgram of pyrrolizidine alkaloids (toxic compounds in comfrey) if taken by mouth. This is a tiny amount. For comparison, one baby aspirin has 80,000 micrograms (or 80 milligrams) of aspirin.

What is the history behind it?

It is reported that comfrey has been used since about 400 BC for wound healing, inflammation, gout, ulcers, gangrene, burns, sprains, and fractures. It also was eaten as a vegetable, much like spinach. In folk medicine, comfrey has been used to treat conditions such as arthritis, colitis, diarrhea, gallstones, and pleurisy. A few practitioners tried using comfrey to treat cancer in the twentieth century.

What is the evidence?

Available scientific evidence does not support claims that comfrey is useful in curing cancer or any other disease. A few recent studies that looked at European creams made from comfrey and comfrey extracts suggested they might be helpful in treating lower back pain, arthritis, and muscle aches when applied to the skin of the affected area. At least one study suggested that very high concentrations of the herb were more helpful than lower concentrations.

When taken internally, comfrey can cause severe liver damage. Several studies have shown that comfrey contains toxic compounds called pyrrolizidine alkaloids or PAs, which can cause severe liver damage. Animal studies have also shown that these chemicals lead to the development of liver tumors.

Are there any possible problems or complications?

This substance may not have been thoroughly tested to find out how it interacts with medicines, foods, herbs, or supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.

The internal use of comfrey is not considered safe. Experts strongly warn consumers not to eat or drink anything that contains comfrey. This herb should be avoided, especially by women who are pregnant or breastfeeding. The U.S. Pharmacopeia (the U.S. compendium of quality control tests and information on drugs) reports comfrey should not be used on broken skin because it may be absorbed into the body.

In July 2001, the FDA advised supplement manufacturers to remove products containing comfrey from the market and alert customers to stop using these products immediately because of the serious health hazards associated with pyrrolizidine alkaloids. The Federal Trade Commission has also taken action against unsafe products containing comfrey. Severe liver damage and even death has occurred with long-term use. Kidney damage is also possible.

Common comfrey can be easily mistaken for other plants in the same family, such as Russian comfrey or prickly comfrey, both of which contain even higher levels of the pyrrolizidine alkaloid toxin. Poisonings have also been reported when foxglove or other toxic plants have been mistaken for comfrey.

Allergic reactions to comfrey, while rare, are possible. Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.

Additional resources

More information from your American Cancer Society

The following information on complementary and alternative therapies may also be helpful to you. These materials may be found on our Web site (www.cancer.org) or ordered from our toll-free number (1-800-ACS-2345).

Dietary Supplements: What Is Safe?

The ACS Operational Statement on Complementary and Alternative Methods of Cancer Management

Complementary and Alternative Methods and Cancer

Placebo Effect

Learning About New Ways to Treat Cancer

Learning About New Ways to Prevent Cancer


Blumenthal M, ed. The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. Austin, TX: American Botanical Council; 1998.

FDA advises dietary supplement manufacturers to remove comfrey products from the market. July 6, 2001. Center for Food Safety and Applied Nutrition. US Food and Drug Administration Web site. http://www.cfsan.fda.gov/~dms/dspltr06.html Accessed June 4, 2008.

Foodborne pathogenic microorganisms and natural toxins handbook: pyrrolizidine alkaloids. January 1992. Center for Food Safety and Applied Nutrition. US Food and Drug Administration Web site. http://www.cfsan.fda.gov/~mow/chap42.html. Accessed June 4, 2008.

Comfrey. British Columbia Cancer Agency Web site. http://www.bccancer.bc.ca/PPI/UnconventionalTherapies/Comfrey.htm. Updated February 2000. Accessed June 4, 2008.

Comfrey. Memorial Sloan-Kettering Cancer Center Web site. http://www.mskcc.org/mskcc/html/69190.cfm. Accessed June 4, 2008.

Comfrey. University of Maryland Medical Center Web site. http://www.umm.edu/altmed/ConsHerbs/Comfreych.html. Updated March 15, 2007. Accessed June 4, 2008.

D’Anchise R, Bulitta M, Giannetti B. Comfrey extract ointment in comparison to diclofenac gel in the treatment of acute unilateral ankle sprains (distortions). Arzneimittel-Forschung. 2007;57:712-716.

Grube B, Grünwald J, Krug L, Staiger C. Efficacy of a comfrey root (Symphyti offic. radix) extract ointment in the treatment of patients with painful osteoarthritis of the knee: results of a double-blind, randomised, bicenter, placebo-controlled trial. Phytomedicine. 2007;14:2-10.

Gruenwald J. PDR for Herbal Medicines. 3rd ed. Montvale, NJ: Thomson PDR; 2004.

Fetrow CW, Avila JR. Professional's Handbook of Complementary & Alternative Medicines. Philadelphia, PA: Lippincott Williams & Wilkins; 2004.

Kucera M, Barna M, Horàcek O, Kàlal J, Kucera A, Hladìkova M. Topical symphytum herb concentrate cream against myalgia: a randomized controlled double-blind clinical study. Adv Ther. 2005;22:681-692.

Ridker PM, McDermott WV. Comfrey herb tea and hepatic veno-occlusive disease. Lancet.1989;1:657-658.

Teynor TM, Putnam DH, Doll JD, Kelling KA, Oelke EA, Undersander DJ, Oplinger ES. Comfrey. Alternative Field Crops Manual Web site. http://www.hort.purdue.edu/newcrop/afcm/comfrey.html. Updated November 17,1997. Accessed June 4, 2008.

Note: This information may not cover all possible claims, uses, actions, precautions, side effects or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for consultation with your doctor, who is familiar with your medical situation.

Last Medical Review: 11/30/2009
Last Revised: 11/30/2009