Drug development regularly has to deal with complex circumstances on two levels: the local level of pharmacological intervention on specific target proteins, and the systems level of the effects of pharmacological intervention on the organism. Different development strategies in the recent history of early drug development can be understood as competing attempts at coming to grips with these multi-level complexities. Both rational drug design and high-throughput screening concentrate on the local level, while traditional empirical search strategies as well as recent (...) systems biology approaches focus on the systems level. The analysis of these strategies reveals serious obstacles to integrating the study of interventive and systems complexity in a systematic, methodical way. Due to some fairly general properties of biological networks and the available options for pharmaceutical intervention, drug development is captured in an obstinate methodological dilemma. It is argued that at least in typical cases, drug development therefore remains dependent on coincidence, serendipity or plain luck to bridge the gap between development methodology and actual therapeutic success. (shrink)