Comfrey liver toxicity

Comfrey (Symphytum officionale). Ointments made from comfrey are used topically for wound and bone healing. Comfrey tea and pills have been prescribed by herbalists to treat gastrointestinal ulcers and diarrhea. However, the FDA advised dietary supplement manufacturers to take comfrey off the market in 2001 because of the gathering evidence that comfrey taken internally causes severe liver toxicity. The FDA also noted the lack of evidence for comfrey s effectiveness. Comfrey should not be used by pregnant women or breastfeeding mothers. 

Nevertheless, Foster and Johnson emphasize that comfrey also contains toxic pyrrolizidine alkaloids (PAs), as documented in Chapter 6. Although PAs will help stop bleeding, the negative effects outweigh the beneficial, for comfrey has been found to cause liver damage and produce cancerous liver mmors. Despite its long history in herbal medicine, no clinical smdies have documented any positive effects attributable to comfrey. Many studies, however, have demonstrated its liver toxicity. 

Pyrrolizidine alkaloid compounds in comfrey have been associated with cases of liver toxicity (see Adverse Events and Side Effects below). The American Herbal Products Association has established a trade requirement (AHPA 2011) that all products with botanical ingredients that contain toxic pyrrolizidine alkaloids, including comfrey, are not offered for sale for internal use and display the following cautionary label "For external use only. Do not apply to broken or abraded skin. Do not use when nursing."... 

Rats fed diets containing 2 or 8% comfrey root for 12 weeks did not develop liver toxicity but did have a higher mutation rate in liver and lung cell genes, and expressed genes that were involved in liver injury and abnormalities, including liver fibrosis and cancer development (Mei et al. 2005,2006 Mei and Chen 2007). 

Some herbal products are very toxic. Comfrey may be an effective treatment for bruises and sprains, but it contains pyrrazolidine alkaloids, which can cause severe liver damage. 

Comfrey is a perennial herb used for the prevention of kidney stones nourishing and repairing bone and muscle and for the treatment of injuries such as burns and bruises. In Australia, comfrey is classified as a poison and its sales have been restricted in several regions. Many different commercial forms of comfrey are marketed, including oral and external products. Commercial comfrey is usually derived from the leaves or roots of Symphytum officinale (common comfrey). However, some products are also derived from Russian comfrey. Russian comfrey contains a very toxic pyrrolizidine alkaloid, echimidine, which is not found in common comfrey. However, common comfrey contains other hepatotoxic alkaloids, namely 7-acetylintermedine, 7-acetyllycopsamine and symphytine. The metabolites of these alkaloids are very toxic to the liver. Ridker et al. documented hepatic venocclusive disease associated with consumption of comfrey root. Long-term smdies in animals have also confirmed the carcinogenicity of comfrey in animal models. ... 

Some have also questioned the safety of comfrey externally. According to one toxicologic researcher (Mattocks, 1980), external use of comfrey should not be hazardous because the PAs must be converted to the toxic free PAs by the liver (Mattocks, 1968). 

Mel, N., L. Guo, L. Zhang, et al. 2006. Analysis of gene expression changes in relation to toxicity and tumorigenesis in the livers of Big Blue transgenic rats fed comfrey (Symphytum officinale). BMC Bioinformatics 7(Suppl. 2) S16. 

PAs are of special interest currently because several of them have been shown to cause clinical toxicity in humans. Comfrey, a well-known medicinal herb, contains PAs that are capable of causing liver damage [19]. 

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