UK drugs group Glaxosmithkline (GSK) has been sued in the US for allegedly lying about the effectiveness and safety of its antidepressant Paxil.
Glaxo is accused of withholding research information on Paxil
New York state attorney general Eliot Spitzer filed the case at the New York State Supreme Court in Manhattan.
The lawsuit claims GSK has deliberately witheld negative information on Paxil, which is also known as Seroxat.
Mr Spitzer also says the company misrepresented study results to its sales force. GSK has denied the claims.
The case centres on the safety of the use of the drug for children and adolescents.
Mr Spitzer says GSK carried out five studies into the matter, but published only one which had mixed results.
He also alleges that the company suppressed negative results from the other studies which did not show Paxil worked and may have even suggested an increased risk of suicide.
Furthermore, the drugs giant engaged in "repeated and persistent fraud by concealing and failing to disclose" the information in medical information letters it sent out to doctors, he said.
Anti-depressants have been making the news recently, amid claims that they increase the risk of suicide or suicidal thoughts in their users.
During 2002, more than two million prescriptions for Paxil were written for children and adolescents in the US.
US regulators have only approved the drug for the treatment of adult depression, but physicians do have the ability to prescribe it for children.
But GSK spokeswoman Mary Ann Rhyne said the allegations were untrue.
She said that all information about the trials was disseminated either in medical journals and public scientific meetings, as well as to regulatory watchdogs.
Mr Spitzer's suit also argues that the company misrepresented the results of its research to its sales representatives, saying it had "remarkable efficacy and safety in the treatment of adolescent depression".
He has demanded that the firm give up all of the profits it has made through the claimed misconduct.
Paxil sales - which are already under pressure from rising generic competition - totalled $291m in the three months to March, with US sales amounting to $148m, Glaxo's latest company report said.
Shares in the group fell 33p to close at 1111p on the London Stock Exchange, while in afternoon trade in New York trade they ended the day at $41.39, a 3% fall.