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.
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.