Evidence that the painkiller Vioxx might increase the risk of heart attacks and strokes emerged nearly four years before the drug was voluntarily withdrawn from the market, research has shown.

Vioxx, the brand name for rofecoxib, was designed to fight the pain of arthritis. It was launched in May 1999 by Merck & Co Inc. But in September 2004, Merck voluntarily pulled Vioxx following a large trial that was halted early after finding evidence linking Vioxx to a raised risk of cardiovascular events.

In November 2004, Merck's then chief executive Raymond Gilmartin testified before a US Senate finance committee that until the halted trial, there was no suggestion from research data that patients taking Vioxx were at increased risk.

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Yesterday, experts from the Mount Sinai School of Medicine in New York writing in the journal Archives of Internal Medicine produced evidence of clear concerns about Vioxx from December 2000 onwards.