Antiviral drugs such as Tamiflu and Relenza that form the cornerstone of the government's fight against swine flu should not be given to those under the age of 12, researchers claimed today.

They called on the Department of Health to immediately reassess its pandemic flu policy after finding that side-effects from medicines such as Tamiflu could outweigh any benefit.

The research, by Dr Matthew Thompson, a clinical scientist and Oxford GP, and Dr Carl Heneghan, a GP and clinical lecturer at Oxford University, found that in some children Tamiflu caused vomiting, which can lead to dehydration and complications.

Thompson said it was "inappropriate" for Tamiflu and Relenza to be given to most children with mild flu symptoms. "The downside of the harms outweighs the one-day reduction in symptomatic benefits," Heneghan said.

The Department of Health said: "While there is doubt about how swine flu affects children, we believe a safety-first approach of offering antivirals to everyone remains a sensible and responsible way forward. However, we will keep this policy under review as we learn more about the virus and its effects."

The study – a peer review of seven trials published by the British Medical Journal – included analysing four studies involving children aged one to 12 taking Tamiflu or another antiviral, Relenza. The children were being treated for normal seasonal flu but the experts behind the research said their findings would extend to the current swine flu pandemic. Thompson said children with mild symptoms should be treated in the same way as if they had any other mild flu – with drinks to cool high temperatures and rest – and that there was no need for children who were otherwise healthy to be taking Tamiflu or Relenza.

The Department of Health said that the review's authors had noted themselves that it was "questionable" how far research into seasonal flu could be used to extend knowledge about swine flu. "We already know that swine flu behaves differently to seasonal flu, and past pandemics have hit younger people hardest," it said.

The department added: "The BMJ research is correct to say that many people with swine flu only get mild symptoms, and they may find bed rest and over-the-counter flu remedies work for them.

"But for those who experience severe symptoms, the best scientific advice tells us that Tamiflu should still be taken as soon as possible – and to suggest otherwise is potentially dangerous. If people are in any doubt about whether to take Tamiflu, they should contact their GP."

The research team also warned parents to be on their guard for any potential complications and signs that their child was getting worse.

For children with compromised immune systems or conditions such as cystic fibrosis, parents may want to discuss the options with their GP. "I think what GPs should do is to weigh up the risks and benefits with the parent," Thompson said.

The researchers likened the current health policy, which saw more than 315,000 courses of antivirals given out during the first fortnight that the national pandemic flu helpline was in operation, as akin to misguided historical health policies such as prescribing antibiotics for sore throats.

"The problem is a resistance issue," said Heneghan. "Going forward we have a treatment which is ineffective because we've given it to everybody. We are calling for a more rational prescription process for these drugs."

The study also found Tamiflu had little or no effect on asthma flare-ups, ear infections or the likelihood of a child needing antibiotics. It comes a little over a week after other research found that children given Tamiflu reported side-effects including nausea and nightmares.

The government has repeatedly referred to its stockpile of antivirals as one reason why people should not be overly concerned about the current pandemic.

Heneghan and Thompson called on the Department of Health to review its current policy. "It's possible a more conservative strategy [like] reserving these anti-viral drugs for people, for children who are more likely to have complications of the illness, might be a more sensible strategy," Heneghan said.

Their study showed the effect of antivirals on reducing the length of illness or preventing complications was likely to be limited.

They added that 13 people need to be treated to prevent one additional case; therefore antivirals reduce transmission by 8%.

The researchers reviewed four trials on the treatment of flu in 1,766 children – 1,243 with confirmed flu, 55% to 69% with type A, the same strain as swine flu – and three trials involving the use of antivirals to limit the spread of flu.