Two teenage boys who took the antiviral drug Tamiflu exhibited abnormal behavior that led to their deaths, with one jumping in front of an oncoming truck last year and the other falling from the ninth floor of a building earlier this year, health ministry and other sources said Saturday.

"This was the first report of a death attributable to abnormal behavior where a causal link with the drug cannot be ruled out," an official at Health, Labor and Welfare Ministry said.

The ministry was notified of the first case, which took place in February 2004, by Chugai Pharmaceutical Co., the Japanese distributor of the prescription medicine made by Swiss drug giant Roche, the official said.