TOKYO, March 27 (Reuters) - Japan plans to keep stockpiling the Tamiflu antiviral drug to tackle any future bird flu pandemic, even though it has warned doctors not to give the drug to teenagers, a Health Ministry official said on Tuesday.

The decision was made at a meeting of experts on Monday, the official said.

Japan plans to stockpile enough doses within the next year to treat 25 million patients and to prevent 3 million people from being infected with the deadly H5N1 avian flu virus.

The virus has swept through poultry across Asia to Africa and Europe. Experts believe it could mutate into a form that would easily pass from one person to another, killing tens of millions of people within months.

The Health Ministry said last Wednesday it had ordered the importer of the drug to warn doctors against giving it to teenagers after two new cases of abnormal behaviour were reported.

Two teenagers were hurt in February and March by falling from buildings after taking the drug, produced by Swiss firm Roche Holding AG <ROG.VX>, the ministry said.

A total of 15 young people have been injured or killed in similar incidents since 2004, the ministry said last week, as concern mounted that Tamiflu, seen as effective against a possible pandemic triggered by bird flu, may induce psychiatric symptoms.

Tamiflu is imported to Japan, the world's heaviest user of the drug, by Chugai Pharmaceutical Co. Ltd. <4519.T>, a Japanese drug maker half-owned by Roche.

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