Comfrey (Symphytum spp.) is native to both Europe and Asia and has traditionally been used as both a food and forage crop. Three plant species in the genus Symphytum are medicinally relevant and include wild or common comfrey (Symphytum officinale L.), prickly or rough comfrey [Symphytum asperum Lepechin (Symphytum asperrimum Donn)], and Caucasian, Quaker, Russian, or blue comfrey [Symphytum × uplandicum Nyman (Symphytum peregrinum Lebed.)], which originated as a natural hybrid of Symphytum officinale L. and Symphytum asperum Lepechin.
Comfrey has traditionally been both applied to the skin (topically) for inflammation, pain and wound healing, and taken by mouth (orally) for gastrointestinal, respiratory and gynecological concerns.
Although evidence supporting oral use of comfrey is lacking, clinical trials suggest topical comfrey may be advantageous for pain and inflammation associated with injuries.
Although comfrey has been traditionally used both orally and topically, recent evidence suggesting carcinogenic and hepatotoxic effects has led to withdrawal of oral products from the market in many countries and warnings to avoid use on open wounds.