Combination therapy of Western drugs and herbal medicines: recent advances in understanding interactions involving metabolism and efflux.

INTRODUCTION: While complementary and alternative medicine markets prosper with an increasing number of consumers of herbal medicines, there is an associated likelihood for herb-drug interactions to occur. Modulation of the activity of metabolic enzymes and/or active transporters by chemical constituents of herbal medicines may influence the therapeutic outcomes of coadministered allopathic medicines due to changes in their pharmacokinetic profiles. Although valuable information on herb-drug interactions is obtained by in vitro studies, such as the mechanisms of interaction, clinical significance of interactions is ultimately demonstrated by in vivo data. AREAS COVERED: The authors outline the mechanisms of herb-drug pharmacokinetic interactions briefly and discuss pharmacokinetic interactions between different therapeutic classes of Western drugs and herbal medicines. Furthermore, the authors also discuss herb-drug interactions from both in vitro and in vivo studies with specific focus on recent findings. EXPERT OPINION: Basic and clinical researches have contributed to the comprehension of the underlying mechanisms involved as well as the practical implications of herb-drug interactions. This provides a foundation for development of guidelines to inform patients about herb-drug interactions that can affect their health.