Comfreys contain livertoxic pyrrolizidine alkaloids. Read more here. -Henriette
A COMMON wild plant, of great virtue; it is frequent by ditch sides; it grows a foot and half high: the leaves are large, long, not very broad, rough to the touch, and of a deep disagreeable green: the stalks are green, thick, angulated, and upright. The flowers grow along the tops of the branches, and are white, sometimes reddish, not very large, and hang often downwards. The root is thick, black, and irregular; when broken it is found to be white within, and full of a slimy juice. This root is the part used, and it is best fresh, but it may be beat up into a conserve, with three times its weight of sugar. It is a remedy for that terrible disease the whites. It is also good against spitting of blood, bloody fluxes, and purgings, and for inward bruises.
The Family Herbal, 1812, was written by John Hill.