Medicines are a great contribution to the rising life expectancy in XX century. But a lot of drug safety problems were reported since 1960's. More recently, ineffectiveness is also being considered as a problem. Since 1975, the term 'drug-related problem' (DRP) is being used for several definition and purposes. This has led to a number of different DRP classifications. The aim of the present review is to gather different positions, definitions and classifications of DRP. And to present a more modern concept, which is also named as pharmacotherapy failure, corresponding to negative clinical outcomes resulting from the use or the lack of use of medicines. Those pharmacotherapy failures include necessity, effectiveness and safety problems.