GlaxoSmithKline (GSK) is facing a US lawsuit alleging that it covered up negative research findings on its anti-depressant drug Paxil.
Paxil is sold as Seroxat in the UK
The lawsuits were filed on behalf of children and teenagers who were prescribed Paxil, known as Seroxat in the UK and Europe.
They claim GSK suppressed data showing that Paxil increased suicidal tendencies in young people.
GSK has denied the allegations, and said it would defend itself in court.
"We have publicly communicated the data in a variety of ways - in peer-reviewed journals, in presentations at major conferences, and in letters to physicians," a GSK spokesman said.
The lawsuit is the latest in series of legal battles GSK has had to fight over Paxil, once its best-selling drug.
Earlier this year, claims that some research into Paxil may have been withheld triggered an investigation by New York prosecutor Eliot Spitzer.
Last month, the company paid $2.5m (£1.3m) to settle Mr Spitzer's inquiry.
It also agreed to publish the results of all clinical tests on its drugs since December 2000 on the internet.
The December cut-off date marks the point at which Glaxo Wellcome merged with Smithkline Beecham.
GSK is also fighting separate lawsuits brought by adult Paxil users who claim it caused adverse side-effects.
GSK shares were down 4 pence at £11.49 in early afternoon trade in London.