The manufacturers of the bird flu drug Tamiflu are about to repeat basic research and clinical trials on the high profile influenza drug.
Swiss drug maker Roche and Japanese partner Chugai will conduct the new research following reports of a possible link to abnormal behaviour in teenagers.
Tamiflu has been under intense scrutiny in Japan following cases of young people jumping from buildings after taking the drug.
Tamiflu is being stockpiled around the world because it is considered the best first line treatment option currently available should there be a bird flu epidemic.
The new research on the antiviral has been called for by the Japanese health ministry amid fears that it may have been linked to several teenagers who killed or harmed themselves during episodes of extreme mental disorder.
In February this year a boy and a girl, both 14, fell to their deaths after taking the drug.
Although the Japanese health ministry says there was no evidence of a causal link between Tamiflu and the behaviour they have ordered doctors not to prescribe it to teenagers, unless they are suffering from extreme flu symptoms.
The ministry has advised Roche and Chugai to begin pre-clinical and human clinical trials to establish whether Tamiflu could be linked to side-effects such as delirium and delusion.
The Japanese also plan to launch their own full investigation into whether there was a causal link between the drug and psychiatric problems.
Of 1,268 cases of patients experiencing side effects after taking Tamiflu, 183 of them, mostly young people, were classified by the ministry as having shown abnormal behaviour.
Both Roche and Chugai deny any such link and doctors say influenza itself can cause abnormal behaviour.