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Interactions between herbs and medicines : St. John's wort

Interacties tussen kruiden en geneesmiddelen : Sint Janskruid


People are increasingly using herbal dietary supplements to improve a wide variety of health conditions. This takes the form of self-medication, sometimes supplemental to regular drug prescriptions. The Dutch Commodities Act prohibits the use of substances that pose a potential health risk. However, using herbal supplements in combination with prescribed medicines can cause an interaction that can either strengthen or decrease the efficacy of a medicine, with potentially adverse health effects. The RIVM (National Institute for Public Health and the Environment) by order of the NVWA (Netherlands Food and Consumer Product Safety Authority), has compiled a 'top ten' list of herbs most likely to cause health risks as a consequence of herbal-drug interactions. This list includes St. John's wort, garlic, ginkgo biloba, valerian, turmeric and green tea. The RIVM also advises the NVWA on the most effective way to communicate these data. In this report data are presented on the interactive effects of the number one on the list: St John's wort. The remaining nine herbs will follow in the near future. For St John's wort, most commonly used to alleviate mild to moderate depression, the largest number as well as the most serious interactions are documented. St. John's wort reduces the efficacy of a number of medicines prescribed for the treatment of fungal and viral infections, for cancer (chemotherapy) and for medicines used to suppress the immune system (in tissue transplants). In contrast, it can also strengthen (unintendedly) the effectiveness of a number of prescribed sedatives. The severity of these side effects depends on both the dose of the drug as well as the dietary herbal supplement. The precautionary advice is not to use St John's wort (either in tea or supplement form) in combination with these prescribed medicines. Due to the potentially harmful effects of the drug interactions, it is important to inform consumers, physicians and pharmacists of the possible risks involved. They also should be able to inform each other about these aspects. Improvements should be promoted to avoid undesirable interactions with herbal dietary supplements.

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