The wound-healing properties of comfrey are partially due to the presence of allantoin, which stimulates cell proliferation and augments wound healing. It has a centuries long reputation for being useful in all hurts and bruises both internal and external, including delayed union of fractures. Comfrey may be used externally to speed wound healing and guard against scar tissue. In deep wounds, caution should be exercised as an external application placed too early can lead to tissue formation over the wound, possibly resulting in an abscess.
Comfrey leaves usually applied externally, while comfrey root decoctions are used internally. To make a decoction, 1-3 teaspoons of dried root are placed in water. Boil the water, let simmer for 10-15 minutes and drink tid. Some 2-4ml of the tincture can be taken with the same frequency. To use the leaves as a poultice just crush them and apply to the wound.
Caution - External Use Only
On July 6, 2001 the FDA issued a letter to communicate their concern about the marketing of dietary supplements that contain the herbal ingredient comfrey - Symphytum officionale (common comfrey), S. asperum (prickly comfrey), and S. x uplandicum (Russian comfrey). These herbs are a source of pyrrolizidine alkaloids and according to the FDA present a serious health hazard to consumers when they are ingested. [Note: evidence suggests that liver toxicity occurs with the internal use of the leaf, but not the root.]
Although there was no evidence for liver damage in a group of people who regularly consumed comfrey, there are a number of case reports that implicate consumption of comfrey in the development of liver disease.