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Many Large Clinical Trials Remain Unpublished

Timothy Platts-Mills

Timothy Platts-Mills (UNC-Chapel Hill)

Medical researchers at University of North Carolina in Chapel Hill found some three in 10 clinical trials having 500 or more participants remain unpublished, with results from the vast majority of unpublished studies not made available on, the U.S. government’s database. Findings from the team led by emergency medicine professor Timothy Platts-Mills were reported online in the British Medical Journal. is the largest registry of clinical studies with more than 154,000 entries from 185 countries. The database was established in 1997 and is maintained by National Library of Medicine at National Institutes of Health (NIH). Trial sponsors are required by the 1997 law to register their studies with the site, which sponsors then update as the studies proceed. In 2007, Congress expanded’s functions, requiring trial sponsors to submit summary results, with penalties ranging from withholding of NIH grant funding to fines of $10,000 a day.

Platts-Mills and colleagues searched clinical studies listed in for studies registered prior to January 2009, with a planned or actual enrollment of 500 or more participants — an arbitrary number, but one for which a study would be considered beyond the pilot stage. The researchers also focused on randomized trials, where participants are assigned at random to different test or control groups, since results of studies conducted under these conditions would more likely meet journals’ criteria for publication.

The team then searched three databases of research publications — PubMed, Google Scholar, and Embase — between April and November 2012 to find published studies with results of clinical trials. The returns from the publications search with clinical trial data were then compared to the results of the search.

The Chapel Hill team found 585 registered randomized clinical trials with 500 or more participants, about three-quarters of which (77%) were late-stage or post-marketing trials, with a total planned or actual enrollment of more than 990,000. Of those 585 studies, 171 or about three in 10 (29%) did not have published results. The non-published studies enrolled nearly 300,000 participants.

About one-third (32%) of the industry-funded trials were among those where results were not published, compared to less than two in 10 (18%) of the studies financed by government or other sources.  Of the 171 non-published trials, the vast majority — 133 or 78 percent — had no results posted on

Legal requirements aside, the researchers say sponsors of clinical trials have an ethical obligation to publish the results of their studies. This principle is embodied in the US Federal Policy for the Protection of Human Subjects, also known as the Common Rule.  “A substantial number of study participants,” say the authors, “were exposed to the risks of trial participation without the societal benefits that accompany the dissemination of trial results.”

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