Research from the UK says negative side-effects from clinical trials are often lost when the study reaches peer review.

Experts from the University of York have compared published and unpublished reports on clinical trials, and found that many recorded side-effects were not reported in published journal articles.

The authors say it is not good enough, and more transparency is needed to create a more complete picture for health professionals, policy makers, and patients.

The clinical benefits of new drugs are usually tested in randomised clinical trials, in which patients are randomly assigned to receive a drug or placebo, before drugs can be prescribed widely.

Adverse events, or side effects, are also routinely collected in such trials, and should be reported in journal articles to give a clear picture of the benefit and risks of new treatments.

Researcher Su Golder of University of York and colleagues systematically gathered studies which compared published reports of clinical studies with unpublished information on the same studies gathered from conference reports, pharmaceutical companies’ clinical study reports and other sources.

The team found that about 64 per cent of side effects would have been missed by readers looking only at published reports about the medical treatments studied.

The authors conclude that full reporting of adverse events in journal articles is essential to allow patients and doctors to assess the balance between the benefits and harms of medical treatments, noting “the urgent need to progress towards full disclosure and unrestricted access to information from clinical trials”.

Their report is accessible here.