In the 1950s pharmacologists came to realise that drug effects on the body are governed by the effects of the body on that drug. This basic concept generated a dichotomy, whereby classical pharmacology was renamed as pharmacodynamics (which studies the effects of drugs on the body) and supplemented with the study of pharmacokinetics (which deals with the effects of the body on the drug). Underlying the pharmacokinetic approach is the basic idea that a pharmacological effect can only be obtained if the drug itself, or an active biotransformation product, reaches and sustains an adequate concentration at the appropriate site of action in the body. The 2 main factors governing this concentration are the dosage of the drug and the fate of the drug in the body, which in its turn is characterised by the absorption, distribution, metabolism and excretion of the drug. However complex the composition of a herbal medicine may be, its bioactive constituents remain chemical entities which have to obey the same pharmacokinetic rules which hold for synthetic molecules. For this reason, we have repeatedly argued that ethnopharmacology (which studies the human use of crude drugs and poisons in a traditional context) deserves a special branch called ethnopharmacokinetics.