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Majority of adverse events in clinical trials remain unpublished

A lower number and smaller range of adverse events were reported in published studies compared with those unpublished, according to data published in PLoS Medicine.

“We identified serious concerns about the substantial amount of unpublished adverse events data that may be difficult to access or ‘hidden’ from health care workers and members of the public,” Su Golder, PhD, in the Department of Health Sciences at the University of York in the United Kingdom, and colleagues wrote. “Incomplete reporting of adverse events within published studies was a consistent finding across all the methodological evaluations that we reviewed.”

Golder and colleagues used 15 databases to identify 28 analyses, of which nine compared adverse event reporting by publication status. According to these nine analyses, 46% of published studies reported adverse events compared with 95% of unpublished studies. In addition, 43% of published studies included adverse event information compared with 83% of unpublished studies.

The researchers found a median of 64% of adverse events would have been missed if readers only looked at published studies.

Eleven analyses compared the numbers of adverse events. In these analyses, there were 24 comparisons of adverse events, including death, suicide and respiratory events. In 18 of 24 comparisons, the number of adverse events was higher in unpublished studies compared with those that were published. In addition, two other analyses showed there were more types of adverse events reported in matched unpublished studies than in published ones.

There were 20 meta-analyses reporting odds ratios or risk ratios for adverse events with and without unpublished data. In 15 of the meta-analyses, including unpublished data increased the accuracy of the data.

The researchers concluded there is strong evidence that suggests most information on adverse events remains unpublished.

“Our review demonstrates the urgent need to progress toward full disclosure and unrestricted access to information from clinical trials,” the researchers wrote. “This is in line with campaigns, such as All-Trials, which are calling for all trials to be registered and the full methods and results to be reported.” – by Will Offit

Disclosure: The researchers reported no relevant financial disclosures.