Trends in Pharmacological Sciences
Research updateComfrey toxicity revisited
Section snippets
Comfrey use restricted
In addition to essential nutrients, comfrey also contains pyrrolizidine alkaloids (PAs). A recent review emphasized the health risks associated with oral consumption of the PAs found in comfrey [2]. The distribution of comfrey in Canada has been restricted, and its use in Germany is limited to external products, provided that normal use results in a daily dose of <100 μg PAs. In the USA, the Food and Drug Administration has requested voluntary compliance for removal of products containing
Human toxicity reports
Although there have been no recent reports of adverse reaction to comfrey, over a decade ago, several cases of veno-occlusive disease (VOD) associated with comfrey ingestion were reported [2]. These case studies support that underlying illness, nutritional status and the concurrent use of hepatotoxic drugs increase the likelihood of VOD development when using PA-containing drugs.
In the clinical setting, hepatic function is commonly assessed by monitoring the serum concentrations of proteins of
Limitations of toxicity research
The conclusion that comfrey is not safe for internal use in humans is primarily based on studies in which high levels of purified PAs were administered to rodents. Systematic toxicity testing or clinical trials have not been performed. Although PA poisoning in humans can occur, this is most commonly a consequence of consumption of plants other than comfrey [13]. Heavy reliance on data obtained from experiments conducted using rodents or from human poisonings by other plants, is probably not an
Concluding remarks
Comfrey is an herbal medicine with a history of effective therapeutic use in humans. It has documented anti-inflammatory and wound-healing properties and many holistic healthcare providers view comfrey as a crucial element in their repertoire of herbal therapies for treating injury and disease in humans. However, because PAs are an intrinsic component of comfrey, its therapeutic use might increase the risk of liver toxicity. Clearly, the risk of hepatic damage during treatment with comfrey will
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