Herbal medicines have been widely used for thousands of years, and now are gaining continued popularity worldwide as a
complementary or alternative treatment for a variety of diseases, rehabilitation and health care. Since herbal medicines contain more than
one pharmacologically active ingredient and are commonly used with many prescribed drugs, there are potential herb-drug interactions.
A variety of reported herb-drug interactions are of pharmacokinetic origin, arising from the effects of herbal medicines on metabolic enzymes
and/or transporters. Such an alteration in metabolism or transport can result in changes in absorption, distribution, metabolism, and
excretion (e.g., induction or inhibition of metabolic enzymes, and modulation of uptake and efflux transporters), leading to changed
pharmacokinetics of the concomitantly prescribed drugs. Pharmacokinetic herb-drug interactions have more clinical significance as
pharmacokinetic parameters such as the area under the plasma concentration-time curve (AUC), the maximum plasma concentration
(Cmax) or the elimination half-life (t1/2) of the concomitant drug alter. This review summarizes the mechanism underlying herb-drug interactions
and the approaches to identify the interactions, and discusses pharmacokinetic interactions of eight widely used herbal medicines
(Ginkgo biloba, ginseng, garlic, black cohosh, Echinacea, milk thistle, kava, and St. John’s wort) with conventional drugs, using various
in vitro, animal in vivo, and clinical studies. The increasing understanding of pharmacokinetic herb-drug interactions will make health
care professionals and patients pay more attention to the potential interactions.