SummaryAs small molecules, the Janus kinase inhibitors have different, dose‐dependent pharmacological binding selectivities, which, however, do not allow reliable statements about the clinical specificity of desired or side effects. It is therefore of particular importance to recognize that the pharmacodynamics of the individual Janus kinase inhibitors as a function of the treated indication is essentially determined by variable levels of regulation of the JAK/STAT signaling pathway and the pharmacokinetic conditions. Against this background, it becomes clear that only clinical trial data in defined indications are suitable for evaluating the efficacy and safety of Janus kinase inhibitors. An uncritical extrapolation of observations regarding efficacy and safety from studies of other indications should therefore only be made with due caution.