Patients' lives are being put at risk and public money wasted on ineffective medicines because researchers are concealing the results of clinical trials amid a "culture of haphazard publication and incomplete data disclosure".
Papers published in the British Medical Journal say researchers who conceal trial results are failing patients who agreed to participate in clinical trials because they believed they would further science.
One BMJ paper, by researchers at the Universities of California and Copenhagen, re-examined conclusions from reviews for nine drugs, including anti-psychotics, an antibiotic and treatments for dementia and migraine, after adding the results contained in unpublished reports provided to the US Food and Drug Administration.
They found that 46 per cent of the positive outcomes had been overestimated, 46 per cent had been underestimated and only 7 per cent were identical when the missing data was considered. The anti-psychotics fared worst: all were less effective and more harmful when unpublished data was included.
An earlier study found that by concealing negative results, the benefits of 12 commonly prescribed antidepressants had been over-egged by an average of 32 per cent.
The BMJ also highlights how researchers conducting systematic reviews often fail to mention missing data in their conclusions, which could further mislead clinicians.
Dr Kate Law, the director of population and clinical research at Cancer Research UK, said some companies deliberately "parked" results they considered to be a "commercial disaster", hoping the drug would later prove effective for a different tumour or a different disease stage.