[Phytotherapeutic medicines. A possible source of drug interactions].

Herbal drugs are popular. Coming from nature, many people are still reluctant to link them with the risk of adverse effects. Many of these products do not require a prescription. Thus, their use and any potential risks may easily escape the physician's attention. Interactions, causing either adverse effects or treatment failures, with synthetic drugs have attracted increasing interest and recent case reports (e.g. about patients suffering from transplant rejection upon using of St John's wort with subsequently insufficient cyclosporine levels) have triggered some systematic research. As of yet, however, a substantial part of knowledge is based on case reports only. In this situation, the assessment of potential risks arising from herb drug interactions is difficult. More research is needed. This review is a brief account of interactions involving garlic, ginkgo, ginseng, echinacea, and St John's wort.