Importance of the field: The global increase in the popularity of alternative medicines has raised renewed concerns regarding herb-drug interactions. These interactions are especially important for drugs with narrow therapeutic indices and may either be pharmacodynamic or pharmacokinetic in nature. Areas covered in this review: Pharmacokinetic interactions which may exist between herbs and drugs, the mechanisms of these interactions with appropriate examples based on primary and secondary data in publications are discussed. The mechanisms covered include those that affect oral drug absorption (e.g. modulation of efflux and uptake transporters, complex formation, gastrointestinal motility and pH) and drug biotransformation (e.g. inhibition or induction of enzymes). What the reader will gain: Knowledge on the mechanisms of herb-drug pharmacokinetic interactions supported by an extended list (Table 1) of these types of interactions for quick reference. A critical evaluation of certain herb-drug pharmacokinetic interactions reported in the scientific literature. Take home message: As the incidence and severity of herb-drug pharmacokinetic interactions increase due to a world-wide rise in the use of herbal preparations, more clinical data regarding herb-drug pharmacokinetic interactions are needed to make informed decisions regarding patient safety.