Medically reviewed on June 7, 2018
What is Comfrey?
Comfrey is a perennial herb found in moist grasslands in western Asia as well as in North America. It has bell-shaped red-violet or yellowish flowers. It may contain small amounts of toxic pyrrolizidine alkaloids.
Symphytum officinale L, S. asperum Lepechin, S. tuberosum L, Symphytum x uplandicum Nyman.
Comfrey also is known as Russian comfrey, knitbone, radix consolidate, bruisewort, blackwort, and slippery root.
What is it used for?
Comfrey has been cultivated as a green vegetable and has been used as an herbal medicine for more than 2,000 years. Comfrey's original name, knitbone, derives from the external use of poultices of its leaves and roots to heal burns, sprains, swelling, and bruises. In Western Europe, comfrey has been used topically for treating inflammatory disorders such as arthritis, gout, and thrombophlebitis, and internally for treating diarrhea. Comfrey has been claimed to heal gastric ulcers and hemorrhoids, and to suppress bronchial congestion and inflammation. Commercial comfrey sale and distribution is restricted in Germany and Canada because of its substantial toxicity.
Therapeutic use of comfrey is limited because of its toxicity. A limited number of clinical trials show short-term efficacy of topically applied, alkaloid-free comfrey preparations in skin abrasions and inflammatory conditions. Although not examined in clinical trials, comfrey may possess antifungal and anticancer activity.
What is the recommended dosage?
Oral use of comfrey is not recommended because of potential liver damage. Additionally, because its alkaloids are absorbed through the skin, use of comfrey as a poultice should not exceed an exposure of 100 mcg/day of the alkaloids. Limited trials have evaluated the effectiveness of alkaloid-free preparations for external use; however, these studies did not examine how much liver damage occurred in patients.
Comfrey is not recommended for internal use because of the liver damage caused by its pyrrolizidine alkaloids. Patients with hypersensitivity or allergic reactions to the plant should also avoid external use. Definitely do not use during pregnancy or nursing, with infants, and if you have liver or kidney disease.
Documented adverse effects (the pyrrolizidine alkaloids, have substantial risk of causing fatal liver damage and can cause abortion). Avoid use.
None well documented.
The internal or extensive topical use of comfrey cannot be recommended because of numerous reports of liver damage.
The Food and Drug Administration (FDA) released an advisory in July 2001 recommending that comfrey products be removed from the market because of cases of hepatic veno-occlusive disease. Comfrey is generally considered unsafe, with numerous toxicological effects in animals and humans.