A Sanofi-Aventis spokesman told Reuters that the company had seen the statement issued by the U.S. law firm that filed the lawsuit, Schiffrin, Barroway, Topaz & Kessler, and that it was "disputing the allegations contained in the statement and plans to vigorously defend itself". Sanofi-Aventis had no further comment.

In a statement available on its website, the law firm said the suit was filed in the U.S. district court for the Southern District of New York "on behalf of all purchasers" of Sanofi-Aventis securities from Feb 17, 2006 through June 13, 2007.

"...the complaint alleges that the company failed to disclose material adverse data concerning Zimulti's tendency to cause a statistically significant increase in psychiatric problems, including suicidal thoughts and actions," the statement said.

On June 13 an advisory committee said the U.S. Food and Drug Administration (FDA) should reject the proposed pill, called Zimulti in the United States, because of concerns it could increase suicidal thinking and depression.

The recommendation triggered a sharp fall in Sanofi's share price in the following days.

This is not the first time Sanofi has faced possible Acomplia-related lawsuits seeking class-action status. In November 2007, U.S. law firm Coughlin Stoia Geller Rudman & Tobbins LLP filed a lawsuit in the U.S. District Court for the Southern District of New York, alleging Sanofi-Aventis misled investors about prospects for Acomplia.