Antiviral drugs are sometimes used in fluImage copyrightSCIENCE PHOTO LIBRARY
The antiviral drug Tamiflu was handed out "indiscriminately" during the last swine flu outbreak, a leading panel of UK scientists has said.
The experts said many thousands of patients had received treatment that may have done no good at all.
They are calling for comprehensive trials during the next pandemic, with some patients receiving the drug and others being given routine care.
The report was put together by the Academy of Medical Sciences.
Together with the Wellcome Trust the team reviewed all recent evidence on Tamiflu.
Their new analysis suggests the antiviral pills are helpful in certain, limited circumstances - for example for people unwell in hospital with seasonal flu.
But when it comes to pandemic flu, researchers say there needs to be much more work to find out if the drugs will provide a good defence.
They are urging hospitals and members of the public to be ready to take part in clinical trials when the next large flu outbreak emerges.