Antiviral drugs such as Tamiflu offer little benefit for many flu patients, a review has concluded.
While most patients do not need the drug, more research is also needed on their use in pandemics, experts said.
The report, from Academy of Medical Sciences and the Wellcome Trust, said antivirals can lead to a reduction in the duration of seasonal flu symptoms by between 14 and 17 hours.
But unless the flu strain is particularly severe or the patient is very ill, the benefits are unlikely to outweigh the risk of side effects.
The report said: “This is a relatively small benefit in a condition that is usually self-limiting and which only rarely leads to serious complications.”
Experts found that antivirals, which include Relenza, do work to cut deaths among patients in hospital, particularly if they are given the drugs within 48 hours of first symptoms.
Public Health England (PHE) guidance says antivirals should only be used for patients with uncomplicated flu who are in specific at-risk groups.
These include pregnant women, elderly people in care homes, and people with suppressed immune systems who would be at risk of complications or death.
Antivirals may be prescribed in hospitals for anyone with suspected flu, the guidance adds.
It also recommends antiviral treatment for patients with complicated flu, regardless of underlying health conditions.
Jeremy Farrar, director of the Wellcome Trust and member of the new report's steering group, said: “The failure to conduct research during the last influenza pandemic has contributed to the current weaknesses in the evidence base and the uncertainty facing clinicians.
“Research on the use of antivirals – in hospitalised patients and in high-risk groups in a serious epidemic or pandemic – is a priority.
“It could help health professionals take the best course of action, which could mean fewer hospitalisations and deaths.”
Carl Heneghan, professor of evidence-based medicine at the University of Oxford, said: “The implications of this report should not be underestimated; the misinterpretation of the evidence to date has wasted scarce resources and led to widespread confusion.”
He said there was a need for more clinical trials to investigate antivirals, including on their benefit for hospital patients suffering flu.