Medicines regulators are monitoring the antiviral Tamiflu after reports from Japan that two teenagers who had taken the drug committed suicide.
European regulators say there is no need to amend product warnings
The European Medicines Evaluation Agency said it was aware of the cases.
But it said there was no evidence there was a direct link between Tamiflu and the teenagers' suicides, and said flu itself could lead to delusions.
Tamiflu, the main weapon against a flu pandemic, is being stockpiled by governments including the UK's.
The incidents in Japan took place in February 2004 and February 2005.
Both teenagers displayed abnormal behaviour before their deaths.
In the first case, a 17-year-old ran out of his house and jumped over a railing, falling into the path of a truck.
In the second, a teenager fell to his death from the ninth floor of his apartment building.
An estimated 33m people around the world have received Tamiflu. During the 2004-05 flu season in Japan, six million took the drug.
Japanese authorities have amended the patient information which comes with the drug to list psychiatric effects, such as delusions, in the list of side effects.
However, a spokesman for the EMEA, said it had not been felt necessary to put similar warnings on the medication labelling in Europe.
He stressed flu itself could lead to such conditions, particularly in the elderly and the young.
He added: "Psychiatric side effects are one of the things that is most closely monitored in relation to all drugs.
"But one of the things that has to be determined in these cases is if there was a causal link between the drug and the teenagers' actions."
The spokesman said it was known one of the teenagers had taken Tamiflu before without any ill effects, but would not reveal which for reasons of patient confidentiality.
And he said the EMEA had evaluated 48 reports of psychiatric side effects from Tamiflu as part of a regular safety review of the drug in July this year.
Most - 28 - of those reports had come from Japan, with 10 coming from the US, five from Canada, three from Germany and two from France.
They related to serious abnormal psychiatric behaviour, such as delirium and hallucinations.
A spokeswoman for Roche, the manufacturers of Tamiflu, said the company was aware of the two Japanese cases involving instances of "abnormal behaviour".
She added: "The information on these two cases has been shared with other regulatory authorities around the world, who have taken them into consideration and made the decision that no change to the summary of product characteristics was warranted.
"These conditions are known complications of influenza and its associated high fever.
"A number of studies have clearly shown that use of Tamiflu does not increase the likelihood of such events occurring in patients with influenza."
The Department of Health has placed an order for 14.6m courses of Tamiflu to cover a quarter of the population in the event of a flu pandemic.
A spokesman said its drugs regulators would review the available evidence on the drug.