Botanical dietary supplements (BDS) are complex mixtures of phytochemicals oftentimes exhibiting complex pharmacology. In today's global economy, the opportunity for exposure to exotic phytochemicals in the form of BDS is significantly enhanced. Formulated as concentrated phytochemical extracts, BDS are vehicles for a host of plant secondary metabolites rarely encountered in the normal diet. When taken with conventional medications, BDS may give rise to clinically significant herb–drug interactions (HDI). Pharmacokinetic HDI stem from phytochemical-mediated induction and/or inhibition of human drug metabolizing enzymes and/or transporters, while pharmacodynamic HDI describe interactions between phytochemicals and conventional medications at the drug receptor level. Despite the tens of thousands of BDS formulations currently on the global market, only a small portion appear to pose significant risks for clinically relevant HDI. One explanation for this paucity of clinically significant HDI hinges upon several idiosyncrasies associated with BDS. This chapter summarizes those BDS that pose clinically relevant HDI whose mechanisms are either pharmacokinetically or pharmacodynamically mediated.
