REUTERS

Between April 1 and August 6 there were 418 reports, of which 125 were received in the last week alone.

The 418 reports detailed 686 suspected adverse reactions, including allergy to Tamiflu and nausea.

The Medicines and Healthcare products Regulatory Agency (MHRA) is collecting data on suspected side effects - not all of which are confirmed as being caused by the drug.

Tamiflu, which is manufactured by Roche, has vomiting and nausea listed as its main side effects on its packaging.

A total of 11 per cent of adults and adolescents taking the drug experience nausea and 8 per cent have vomiting, according to the summary of product characteristics.

Headaches are another side effect when the drug is taken preventatively rather than as a treatment.

In children, the most commonly reported side effect is vomiting, with 15 per cent suffering it and 10 per cent having diarrhoea.

A total of 3 per cent of children will get nausea and 5 per cent have reported abdominal pain.

Clinical studies accepted by health bodies in the UK and worldwide show that the drug should not aggravate asthma.

A total of 4 per cent of children with asthma experienced worse asthmatic symptoms when taking the drug - the same proportion as in a group of asthmatic children taking a dummy drug.

The study, on 334 asthmatic children aged six to 12, found the drug did not help cut the length of the illness.

But by the last day of treatment (day six) the lung function was better in children taking Tamiflu, with their Forced Expiratory Volume having increased by 10.8 per cent compared with 4.7 per cent among those on the dummy drug.

The Government has 23 million treatments of Tamiflu and 10.5 million treatments of another anti-viral, Relenza.

Orders of Tamiflu have been placed to increase UK supplies to 50 million doses, enough to treat 80 per cent of the population.

Pregnant women should take Relenza, which is inhaled and helps reduce flu symptoms without affecting the baby.

However, if a pregnant woman has unusually severe flu, a doctor may prescribe Tamiflu.

An expert group reviewed the risk of anti-viral treatment in pregnancy and told the Government the risk was extremely small - smaller than the risk posed by the symptoms of swine flu.

Some people have had wheezing or serious breathing problems when they have used Relenza and it is not recommended for people with asthma or other serious lung problems.

Other possible side effects of Relenza include headaches, diarrhoea, nausea and vomiting.

The MHRA has received a total of 10 reports of side effects from Relenza since April 1.

An MHRA spokesman said: “We have allocated a dedicated section of our website to receive reports of side effects to Tamiflu and Relenza from doctors and the public in order to spot any developing trends.

“We have set up this specific site so that people can log on and report any potential side effects.

“This will assist us in monitoring the safety of these anti-viral medications.

“A report of a reaction does not mean it has been caused by the drug in question - a mere suspicion will suffice.

“The MHRA is very keen to promote this website as we want people to know about it and use it - http://swineflu.mhra.gov.uk/.”