A head injury treatment used for the past 30 years could be killing rather than saving patients, experts warn.
The patients fared better without steroids
A Medical Research Council study of more than 10,000 patients found giving anti-inflammatory drugs to reduce brain swelling increased the risk of death.
The London School of Hygiene and Tropical Medicine scientists told doctors to stop using these drugs to treat people with head injuries.
More data is expected from the trial, which is published in the Lancet.
The effect of the anti-inflammatory drugs, called corticosteroids, on disability six months after head injury would be reported soon, the researchers said.
Their current findings showed the drugs increased the risk of death by about 20% within two weeks of patients with head injuries being admitted to hospital.
The study involved patients treated at 239 hospitals in 49 countries around the world.
Half of the 10,008 patients were randomly allocated to receive corticosteroid treatment. The other half were given a dummy drug.
There were 156 more deaths in the steroid group than in the fake drug group, which was the opposite of what the researchers had expected based on previous smaller studies.
Commenting on the findings in an editorial to the Lancet, Dr Stefan Sauerland from the University of Cologne in Germany, said the results were "a complete and alarming surprise for us all."
"In future, we should avoid trusting in underpowered clinical trials," he said.
Change in practice
Lead researcher Dr Ian Roberts said: "Obviously we'd have preferred to find out that corticosteroids improve patients' chances of surviving head injury.
"But our results are important because they'll improve patient care and protect thousands of future patients from increased risk of death from corticosteroids."
He said it also raised the question of whether these drugs might be harmful for patients with spinal injuries.
Professor Colin Blakemore, chief executive of the MRC, said: "This is an excellent example of how research evidence contributes to changing clinical practice with the potential to improve patient care."
The team is putting together proposals to trial other potential treatments, in particular treatments for excessive bleeding which accounts for most trauma deaths worldwide.
About three million people worldwide die from trauma every year.
Of those who survive to reach hospital, blood loss accounts for many of the subsequent deaths.
Peter McCabe, chief executive of Headway, the brain injury association, said: "There is a real lack of comprehensive research into brain injury.
"We welcome any new research that will help throw light on ways to improve people's survival rates and long-term outcome."