Among the pharmacokinetic concepts, the elimination half-life is most frequently used to describe the fate of a drug in the organism. The fact is often neglected, that the half-life depends on various physiological processes (organ clearances, distribution, occasionally absorption or binding to macromolecules). In many situations, the half-life has little to do with the duration of the effect which may depend on effective concentrations, equilibration delays at site of action, indirect response mechanisms, tolerance, or appearance of active metabolites. Finally, the half-life represents an ambiguous criterion for the choice of drugs: short (or long) half-life can be considered either advantageous or disadvantageous, according to endpoints selected.