Clinical studies can be more or less transparent in four areas: (a) study registration, (b) results reporting, (c) data/code sharing, and (d) study-related documents. This discussion paper explains the extent to which the EU Regulation 536/2014 (Clinical Trials Regulation - CTR) has already positively impacted the area of results reporting in interventional drug trials and how it can improve the availability of study-related documents for independent research in the future. As this positive trend exists only for the area of results reporting and for the subset of interventional drug trials addressed by the CTR so far, a problematic two-class transparency seems to be developing that distinguishes between clinical studies addressed by the CTR and the other clinical studies. Independently of the CTR, academic institutions, funders, and ethics committees should therefore address all four abovementioned areas of transparency in all clinical studies. Monitoring the implementation of transparency in clinical studies would be an important first step in order to specify the need for action. An innovation in the context of transparency of clinical trials could also arise from the fact that the new EU Portal Clinical Trials Information System (CTIS) according to the CTR makes study-related informed consent documents, study protocols, and the investigator's brochures more transparent. This would for the first time open up the opportunity of independent research and quality assurance on issues of informed consent and harm-benefit assessment in clinical research.
