Comfrey is a high-yielding leafy green plant that has been used for centuries as a feed crop for animals and a medicine for humans. However, in 2001, it was removed as an oral dietary supplement from the U.S. market, and, soon afterwards, as a commercial animal food source. These actions were taken because comfrey contains dangerous levels of toxic pyrrolizidine alkaloids and its use has led to severe liver injury and death.
Traditionally, oral or topical use of comfrey was said to help bones heal more rapidly, and this is the origin of its Latin name Symphytum (drawing together). It was also used orally for the treatment of digestive and lung problems. Topical comfrey creams have been used to treat minor wounds, bruises, sprains, and varicose veins.
What Is Comfrey Used for Today?
The active ingredients in comfrey are not known, but may include rosmaric acid, choline, and allantoin.
The tested form of topical comfrey contains 10% of a 2.5:1 juice extract made from fresh pressed plant sap; in other words, every 100 grams of cream contains the equivalent of 25 grams of comfrey sap.
The main form of liver disease seen with comfrey is a blockage of small veins that can lead to liver cirrhosis and eventually liver failure (hepato-occlusive disease). Liver transplantation may be required. Oral use of comfrey for as brief a time as 5 to 7 days in a child and 19 to 45 days in adults has resulted in severe liver disease and death. Long-term use of very low dosages may also cause harm.
In general, the root of the plant contains more pyrrolizidine alkaloids than the leaves. Related species of comfrey such as Symphytum uplandicum and Symphytum asperum contain even higher levels of these toxins, and may be mistakenly sold as ordinary comfrey.
Pyrrolizidine alkaloids in comfrey can be absorbed through the skin. For this reason, it has been recommended that when using comfrey preparations, the daily amount of pyrrolizidine alkaloids should not exceed 100 mcg. Unfortunately, few products are labeled to indicate their pyrrolizidine alkaloid content. Furthermore, the common analytic methods used for testing pyrrolizidine alkaloid content may fail to measure a certain chemical form of these toxins (the N-oxide form), leading to results that are too low by a factor of ten or more. For all these reasons, it may be prudent to avoid topical comfrey products entirely. If you nonetheless wish to use comfrey as a topical treatment, we recommend the following general guidelines:
- Do not apply comfrey for more than 4-6 weeks per year.
- Do not use for more than 10 days in a row.
- Do not apply to broken skin.
In addition, comfrey should not be used by children, pregnant or nursing women, or people with liver disease.
- Reviewer: EBSCO CAM Review Board
- Review Date: 09/2014 -
- Update Date: 09/18/2014 -