Comfrey (Symphytum officinale L.) is a perennial herb of the family Boraginaceae with a black, turnip-like root and large, hairy broad leaves that bears small bell-shaped white, cream, purple or pink flowers. Contemporary herbalists view comfrey as an ambivalent and controversial herb that may offer therapeutic benefits but can cause liver toxicity. One of the country names for comfrey was ‘knitbone’, a reminder of its traditional use in healing. Modern science confirms that comfrey can influence the course of bone ailments. The herb contains allantoin, a cell proliferant that speeds up the natural replacement of body cells. Comfrey was used to treat a wide variety of ailments ranging from bronchial problems, broken bones, sprains, arthritis, gastric and varicose ulcers, severe burns, acne and other skin conditions. It was reputed to have bone and teeth building properties in children, and have value in treating ‘many female disorders’. In past times comfrey baths were popular to repair the hymen and thus ‘restore virginity’. Constituents of comfrey also include mucilage, steroidal saponins, tannins, pyrrolizidine alkaloids, inulin, vitamin B12 and proteins. The flowers of Russian comfrey Internal usage of comfrey should be avoided because it contains hepatotoxic pyrrolizidine alkaloids (PAs). (Note: there are also non-hepatotoxic pyrrolizidine alkaloids.) Use of comfrey can, because of these PAs, lead to veno-occlusive disease (VOD). VOD can in turn lead to liver failure, and comfrey, taken in extreme amounts, has been implicated in at least one death.[6] In 2001, the United States Food and Drug Administration issued a warning against internal usage of herbal products containing comfrey. [7] There are ways to remove the pyrrolizidine alkaloids from comfrey, and some herbal product manufacturers have begun doing so (although the products will still be labelled “for external use only”).[citation needed] Excessive doses of Symphytine, one of the PAs in comfrey, may cause cancer in rats.[8] This was shown by injection of the pure alkaloid. The whole plant has also been shown to induce precancerous changes in transgenic rats.