The pharmaceutical giant is said to have paid-off three generic drugs companies to delay introducing their cheaper generic versions of GSK’s blockbuster drug, Seroxat.

The companies were each attempting to supply a similar generic product in competition to GSK’s branded paroxetine product.

However, in each case, GSK challenged the generic companies’ with allegations that their products would infringe GSK’s patents.

According to the OFT, to resolve these disputes, each of the generic companies were given ‘substantial payments’ to delay releasing their versions of the drugs.

Ann Pope, senior director of services, infrastructure and public markets at the OFT, said: “The introduction of generic medicines can lead to strong competition on price, which can drive savings for the NHS, to the benefit of patients and, ultimately, taxpayers.

“It is therefore particularly important that the OFT fully investigates concerns that independent generic entry may have been delayed in this case.

“No assumption should be made at this stage that there has been an infringement of competition law. We will carefully consider the parties’ representations to the Statement of Objections before deciding whether competition law has in fact been infringed.”

A spokesperson from GSK said: “GSK supports fair competition and we very strongly believe that we acted within the law, as the holder of valid patents for paroxetine, in entering the agreements under investigation.

“These arrangements resulted in other paroxetine products entering the market before GSK’s patents had expired.

“We have cooperated fully with the Office of Fair Trading in this investigation, which covers activities that happened between 2001 and 2004. The paroxetine supply agreements under investigation were terminated in 2004.”

GSK also points out that the OFT’s investigation is covering ground that was already investigated by the European Commission in 2005-2006. The EU investigation did not result in any sanctions against the pharmaceutical company.

The three generic companies that are said to have made these deals with GSK are Alpharma Limited, Generics Limited and Norton Healthcare Limited.