Lawyers for Merck & Co have told the US Supreme Court that investors shouldn't have waited so long to sue the drug maker over warnings about the risks of its painkiller Vioxx.

Merck wants the high court to overturn a decision lower court decision to allow a class-action lawsuit related to value lost in shares after Merck pulled Vioxx off the market.

It will now be up to the the Supreme Court to help clarify the legal standards for determining when a two-year window closes for investors wanting to sue a company accused of defrauding them.

Vioxx was withdrawn from the market on September 30th, 2004, because it was said to double the risks of heart attack, stroke and death.

After it pulled Vioxx from the market, Merck was hit with a lawsuits from shareholders and patients.

Merck has said the investors should have known from public information that there could be problems with Vioxx, after FDA warnings to Merck about Vioxx risks late in September 2001.