Interactions between herbs and conventional drugs: overview of the clinical data.

This article provides an overview of the clinical evidence of interactions between herbal and conventional medicines. Herbs involved in drug interactions--or that have been evaluated in pharmacokinetic trials--are discussed in this review. While many of the interactions reported are of limited clinical significance and many herbal products (e.g. black cohosh, saw palmetto, echinacea, hawthorn and valerian) seem to expose patients to minor risk under conventional pharmacotherapy, a few herbs, notably St. John's wort, may provoke adverse events sufficiently serious to endanger the patients' health. Healthcare professionals should remain vigilant for potential interactions between herbal medicines and prescribed drugs, especially when drugs with a narrow therapeutic index are used.