Following the meeting of an expert group in February, 2002, the International Agency for Research on Cancer (IARC) just published its evaluation of the carcinogenic risks for humans of some herbal plants and emphasizes that natural is not necessarily synonymous with healthy.
Traditional herbal medicines encompass an extremely diverse group of preparations. In recent years, such products have become more widely available commercially, especially in developed countries, where mixtures prepared from leaves, roots, and other parts of exotic plants are imported from various sources and sold for medicinal purposes. These herbal products are marketed for uses, for example weight loss regimens, that were never contemplated in the traditional healing systems from which they emerged. The toxic properties of these preparations are in most cases not well known, and in many countries that import these products herbal medicines are not subject to rigorous standards with respect to manufacturing, efficacy, quality and safety.
At the close of the expert meeting in February, 2002, the IARC concluded that herbal remedies containing plant species of the genus Aristolochia (e.g. European birthwort) were carcinogenic to humans. In 1992, an outbreak of rapidly progressing kidney failure afflicted more than 100 people in Belgium, mostly women, who were undergoing a body-weight loss regimen that involved consuming a mixture of Oriental herbs. In addition, consumption of the herbal mixture caused tumours of the renal pelvis, the ureter and the urinary bladder. Additional cases have subsequently been reported from at least five other countries in Europe and Asia. These herbal mixtures, possibly by accident, contained plants of the genus Aristolochia, which are traditionally considered medicinal plants in China but which contain mixtures of aristolochic acids which were classified as probably carcinogenic to humans.
The IARC Monograph also discusses herbs containing anthraquinone derivatives that have been widely used as laxatives. Epidemiological studies on the relation between the use of these preparations and human cancer incidence are weak and show no association, although in animal experiments 1-hydroxy-anthraquinone induces tumours in rats. Therefore, this compound is classified as possibly carcinogenic to humans. The herb Madder root (Rubia tinctorum), which contains the anthraquinone lucidin, is considered not classifiable as to its carcinogenicity to humans, on the basis of slight increases of the number of tumours in a single study in rats.
The pyrrolizidine alkaloid riddelliine is found in Senecio riddellii and other Senecio species, including S. longilobus, which is used as a herbal tea in certain regions of the world. Although no epidemiological data relating the use of herbal preparations containing riddelliine to cancer incidence in humans are available, riddelliine is clearly carcinogenic in rodents. It is therefore classified as possibly carcinogenic to humans.
IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol. 82, Some Traditional Herbal Medicines, some Mycotoxins, Naphthalene and Styrene, available from IARCPress, orders to: or, from North America, to:
The IARC Monographs
The IARC Monographs series publishes authoritative independent assessments by international experts of the carcinogenic risks posed to humans by a variety of agents, mixtures and exposures. Since its inception in 1972, the series has reviewed more than 880 agents, and IARC Monographs have become well-known for their thoroughness, accuracy and integrity.