[Limits and benefits of non-controlled therapy-related observations]

In the age of evidence-based medicine, results from prospective controlled interventional studies are awarded the highest priority for determining the efficacy of a therapeutic measure. In contract, the role of non-controlled therapy-related observations is very low. This conception is due to the fact that in the absence of a control group it is impossible to assess a causal relationship between an administered therapy and the subsequent clinical outcome.Nevertheless, non-controlled therapeutic observations may be clinically relevant. Four domains may be distinguished : besides their importance for learning and teaching, such observations can contribute to evaluate which benefits results gained in controlled studies have in daily practice. On the other hand, they may point to hitherto unknown phenomena, such as the detection of new indications or unexpected therapeutic side effects. Finally, they may act as an important source for the generation of hypotheses about therapeutic measures, thus fostering further research.