Most problems occurred in Japanese children taking the drug. Japan is the largest market in the world for flu medications because doctors there prescribe drugs like Relenza as a standard treatment for flu symptoms.
The new Relenza label stresses that there is no causal link between Relenza and the psychiatric problems.
London-based Glaxo alerted doctors to the changes in a letter last month, which the FDA posted to its Web site.
Swiss drug maker Roche made similar changes to the label for its drug Tamiflu last month. Tamiflu was the top-selling flu medication worldwide last year with sales of $2.4 billion.
Relenza had sales of $520 million.
Shares of GlaxoSmithKline rose 40 cents Wednesday to $44.60.