A Tamiflu study done in Japan has not eased doubts about the flu drug's safety and possible side effects. Over half of all influenza patients in Japan exhibiting abnormal behaviors had taken the drug Tamiflu; however, it is still not clear if there was a causal link between the drug Tamiflu and their actions, a government report showed on Monday. Japan is investigating whether there is any link between Tamiflu, made by Roche Holding AG, and neuropsychiatric problems after more than 100 people, mostly young people, exhibited erratic behaviors after taking the drug, such as jumping from buildings. There have been a total of eight cases of death after abnormal or possibly abnormal behavior. The Health Ministry report indicated that of the 137 patients who had shown abnormal behavior, 82 had taken Tamiflu, while 52 had not.

But the report, compiled by a group of doctors and other health experts, explained that their figures were difficult to assess because it was not clear what percentage of all influenza patients had been prescribed Tamiflu. The report also said that the number of patients showing abnormal behavior did not drop following the government's warning in March against prescribing Tamiflu to those aged 10 to 19.

A Health Ministry official said that the study had been inconclusive but that a separate group of doctors and experts would present their own study later in the month, saying that they hope to reach some kind of conclusion at that time.

Tamiflu is taken for the treatment of regular seasonal influenza symptoms and is recognized as one of the best defenses against possible bird flu pandemic. According to recent research, Tamiflu successfully suppress the avian flu virus, which public health experts say threatens to cause a world flu pandemic. The tests, which were conducted on 80 mice, demonstrated that Tamiflu could kill the newest strain of the H4N1 virus that infected poultry in Vietnam, Cambodia, and China. Researchers reported a 50%-80% survival rate in mice administered high doses of the drug.

Conversely, public health officials do not paint a promising picture, saying that if the avian flu were to begin spreading rapidly among humans, they would need to know whether the antiviral drugs could prevent and treat the avian flu, because in the early stages of a global outbreak most people would be unvaccinated.

Officials claim it would take months to manufacture and distribute the medication. Experts also fear the new, ever-morphing strains of the virus are more dangerous than the 1997 version that killed six people in Hong Kong. The disease has killed over 50 people in Asia. In an effort to prepare for a pandemic, governments are stockpiling Tamiflu.

Roche and its Japanese partner Chugai Pharmaceutical Co. Ltd. have said that no causal relationship has been established between Tamiflu and the neuropsychiatric symptoms. They argued that doctors say influenza itself can cause abnormal behavior.

Tamiflu, known generically as oseltamivir, is widely prescribed in Japan. Chugai estimates some 35 million people have taken the drug, accounting for around 70 percent of the world's Tamiflu consumption.