Concerns are rising over side effect of bird flu drug Tamiflu on teenagers.

Tamiflu is Swiss-based Hoffman-La Roche's antiviral for general influenza A and B but is also used to combat bird flu. New worries are surfacing about this antiviral drug causing mental disorders among teenagers.

With fear of the H5N1 virus sweeping most east asian nations, governments have doubled the quantity of the drug in storage, as it is the most effective treatment against avian influenza.

Whether to prescribe the pills with risks of side-effects such delusions or other disorders is being widely discussed among medical experts.

Although the drug has been the only medicine accredited to be effective against the H5N1 virus strain by the World Health Organization (WHO), the Japanese and Korean governments restricted its being prescribed to teenagers last year.

The Korean Food and Drug Administration recently announced that the drug should not be prescribed to those between 10 to 19 years old except for emergencies.

There have been 1,268 cases of extraordinary behavior reported in Korea, of which 85 percent were from teenagers. Included were horrifying stories of teenagers reportedly committing suicide by jumping out of buildings or into cars after taking the medicine.

Health experts admit to the dilemma and said when necessary, it should be prescribed with extra prudence.