Japan´s Health Ministry said on Wednesday it had ordered the importer of the bird flu drug Tamiflu to warn doctors against giving it to teenagers after two new cases of abnormal behavior were reported.

Two teenagers injured themselves in February and March by falling from buildings after taking the drug, produced by Swiss firm Roche Holding AG, according to a ministry news release.

A total of 15 young people have been injured or killed in similar incidents since 2004, Kyodo news agency reported the ministry as saying later.

The cases have fueled concern 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, a Japanese drugmaker half owned by Roche.

"As well as changing the warning distributed with the drug, we have directed Chugai Pharmaceutical to raise awareness among medical professionals of the risk of abnormal behavior after taking Tamiflu," the release said.

CAUSAL LINK UNCLEAR

The new warning is to include the words: "Except in cases judged to be high risk, avoid prescribing this drug to minors over the age of 10."

The text will also instruct doctors to tell those caring for children taking Tamiflu not to leave the patients alone.

Media reports said the Health Ministry rejected criticism that it had not acted swiftly enough. Most of the more than 100 reported cases of potentially Tamiflu-related psychiatric problems have been in Japan.

The Health Ministry has said 54 people have died in Japan while taking the drug, but there has been no direct causal link.

"We have not been ignoring the problem. We have made the best decisions at each stage, amid a lack of clarity about the causal relationship," Kyodo news agency quoted the ministry´s drug safety division as saying.

No one was available for comment at the Health Ministry, which made the announcement in the early hours of Wednesday, a holiday in Japan.

The move came after Roche said on Tuesday that new data from Japan and the United States indicated that there was no established causal link between Tamiflu and psychiatric symptoms.

"We have advised Roche of the warning," said a spokesman for Chugai Pharmaceuticals.

"Since patients taking Tamiflu have exhibited abnormal behavior and fallen from buildings, we must accept this procedure. We want to raise awareness as quickly as possible," he added.

Shares in Chugai Pharmaceutical fell in February after police began an investigation into the death of one of the teenagers who had taken Tamiflu.

Chugai shares closed down 0.17 percent at 2,980 yen on Tuesday.