When the patent of a small molecule drug expires generics may be introduced. They are considered therapeutically equivalent once pharmaceutical equivalence (i.e. identical active substances) and bioequivalence (i.e. comparable pharmacokinetics) have been established in a cross-over volunteer study. However this generic paradigm cannot be applied to complex drugs as biologics and a number of other therapeutic modalities. For copies of biologics the European Medicine Agency and other regulatory agencies have introduced a new regulatory biosimilar pathway which mandates clinical trials to show therapeutic equivalence. However for other complex drugs such as the iron-carbohydrate drugs, low molecular weight heparins (LMWHs), liposomal drugs and the glatiramoids regulatory guidance is still mostly lacking. In this paper we will discuss (therapeutic) experience obtained so far with these different classes of 'complex drugs' and their specifics to provide scientific arguments and criteria for consideration for a regulatory framework for the market authorization for these type of drugs.