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Published: Kem. Ind. 60 (6) (2011) 343–349
Paper reference number: KUI-21/2010
Paper type: Professional paper
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Interactions between Herbal Medicinal Products and Conventional Drugs

J. Cvek and S. Tomić


Herbal medicines are traditionally considered natural and therefore safe products, but their increased consumption also increases the potential risk of interactions with conventional medicines and adverse reactions. Adverse reactions of herbal medicinal products may also occur because of the innate herbal toxicity, biological or chemical impurity of the raw herb, misrecognition and substitution with toxic herbal species or counterfeiting using cheaper substances or undeclared synthetic pharmacologically active substances. Numerous interactions of herbal and conventional medicines have been recorded, but for many of them the exact underlying pharmacological mechanisms have not been studied well nor has their clinical significance been established. Some of the better-known interactions are the ones in which the herbal medicine, such as St. John’s wort, induces the hepatic enzyme CYP system responsible for metabolic transformation of many drugs, and therefore causing potentially serious and clinically relevant adverse reactions. For example, this type of interaction between St. John’s wort and an immunosuppressant can lead to a decrease in the mass fraction of the immunosuppressant with consequent transplant rejection. For many of the widely used herbal medicinal products, e. g. Ginkgo, possible interactions can be expected based on published case reports. An example of a recommendation derived from case reports is the one by which the concomitant administration of Ginkgo and anticoagulant drugs (acetylsalicylic acid, warfarin) should be avoided due to increased risk of bleeding. For a relatively small number of herbal medicinal products the active principles and mechanisms of action are known and can therefore be used to predict possible interactions with other medicines. For example, hydroxyanthracene derivatives of Senna, along with other effects, can cause electrolyte excretion that can lead to toxic effect of cardiac glycosides, antiarithmics and potassium depleting drugs (e. g. non-potassium sparing diuretics). In the conditions of the ever-increasing consumption of herbal medicines, it is necessary to increase the level of consciousness and knowledge of interactions between herbal and conventional medicines in order to minimize the risk of interactions and consequential development of adverse reactions. In addition, it is of great importance to report all suspected adverse reactions to herbal medicinal products, as well as interactions and ineffectiveness, to the competent authority in order to contribute to the better understanding of the effectiveness and safety profile of a particular herbal medicinal product.

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herb-drug interactions, herbal medicines, adverse reactions, St. John’s wort