The Food and Drug Administration in the U.S. (FDA) is recommending that patients who take Tamiflu be closely monitored for signs of abnormal behaviour.
The announcement is the latest update on the drug which is currently the first line of defence should a bird flu pandemic erupt, and comes as a result of 12 deaths and psychiatric symptoms among users in Japan.
Of the 103 reported new cases of delirium, suicidal behaviour and other mental problems between August 2005 and July 2006, three cases were fatal.
Ninety five of the cases were apparently Japanese children treated with the drug.
The agency's review found that of the 12 deaths there was one suicide, four cases of sudden death and four cases of cardiac arrest.
There were 32 reports of psychiatric "events" among children, including hallucinations and abnormal behaviour and in two cases a 12-year-old and 13-year-old jumped out of second-floor windows of their homes after taking the medication.
The U.S. and European agencies have emphasised that no causal link has been identified between the use of Tamiflu and reported deaths and the FDA says the updated label was "intended to mitigate a potential risk associated with Tamiflu".
The FDA recommends that close monitoring begin immediately after starting treatment with the drug because of the reports.
The U.S. labels will in future be more in line with the Japanese which already carry a warning that abnormal behaviour could occur.
The current FDA-approved labels only mention that "seizure and confusion" are seen in some patients.
Tamiflu is made by the Swiss pharmaceutical company Roche who deny there is any evidence the drug causes such neuropsychiatric adverse effects.