GlaxoSmithKline (GSK) is facing a class action lawsuit in the US from investors who allege it concealed problems with its anti-depressant drug Paxil.
Paxil is also marketed under the Seroxat label
They allege the firm violated securities laws by issuing "false or misleading public statements".
It comes after studies found Paxil could increase the risk of suicidal behaviour in adolescents.
GSK, which is also facing patient lawsuits over Paxil, said the allegations were "without merit".
A spokesman for GSK, which in the past has defended the way it presented clinical research on Paxil, added that the company had not yet been served with a copy of the lawsuit.
US legal firm Schatz & Nobel said the case was filed on behalf of investors who bought GSK shares traded on the New York Stock Exchange between 21 February 2001 and 5 August 2004.
It claims Glaxo "improperly concealed deficiencies" with Paxil - which is also sold under the name Seroxat - in the treatment of adolescents.
The drug used to be GSK's top-selling product but sales have slowed with the release of cheaper generic versions of the treatment.