Since 2004, adherence to Good Clinical Practice has been mandatory for all clinical drug trials. This was new to the investigator-initiated trials. Our study showed no association between the implementation of the Directive and investigator or industry-initiated trials. However, a steady decline was observed over the entire period. Presumably, the introduction of GCP did not entail a decline because of the presence of GCP units at university hospitals. Thus, researchers can conduct clinical drug trials under the same regulations as drug companies