Also, the leaves and roots of comfrey have been shown to be carcinogenic. PAs from comfrey given to rats caused mortality. Liver pathology was characteristic of PA toxicosis. There are species differences in susceptibility to PAs. Horses and cattle are most commonly poisoned by PAs, while sheep are much more resistant.
Goats are more susceptible than sheep, and pigs are more susceptible than cattle and horses.
Poisoned cattle may have a bloated appearance. Further information on PAs and species differences is presented in Cheeke 1998. Return to Index Uses and Efficacy Comfrey has been promoted and used as a medicinal plant for years. However, no published studies could be found to support the medicinal claims. In the Philippines, the leaves are made into a decoction and used as a drench for swine to treat fevers.