Clinical trial transparency: many gains but access to evidence for new medicines remains imperfect.

BACKGROUND: Although selective and incomplete publication is widely acknowledged to be a problem, full access to clinical trial data remains illusive. SOURCES OF DATA: Authors' personal files, key documents from Food and Drug Administration and European Medicines Agency and focussed searches of PubMed. AREAS OF AGREEMENT: Existing sources of information provide an incomplete overview of scientific research. AREAS OF CONTROVERSY: Persistent arguments about commercial confidentiality and the potential difficulties in de-identifying raw data can block important progress. Current industry efforts are voluntary and only partially satisfy the need for complete data. GROWING POINTS: Requirements for trial registration are increasing. Important regulatory changes in particular in Europe have the potential to result in the release of more information. AREAS TIMELY FOR DEVELOPING RESEARCH: Documenting the effects of prospective trial registration and requirements for proactive clinical trial publication on healthcare decisions, public health and rational resource allocation.