Merck’s pain-killing arthritis drug Vioxx (rofecoxib) can still increase the risk of heart attack, stroke and death a year after patients have stopped taking the medicine, a study has found.

Published online by The Lancet, the study, funded by Merck, shows “the risk was increased close to twofold, and the risk persisted for approximately a year”, co-author Dr Robert Bresalier said.

The new study followed about 2000 people who had been involved with the three-year APPROVe trial that had been intended to show that Vioxx, a COX-2 inhibitor, could prevent the recurrence of colon cancer.

However, the APPROVe trial was cut short by two months after results started to show there was a doubled risk of heart attack, stroke and death in patients taking Vioxx compared with a placebo. Merck pulled the drug from the market in September 2004.

According to the new study, former Vioxx users had a 79% increased risk of cardiovascular complications and death a year after they had stopped taking the drug, than the placebo group. The risk of heart attack or stroke of former Vioxx patients was double that of the placebo group and the risk of death was 31% higher.

The researchers also found that the higher risk started in a relatively short time after taking the drug, despite Merck insisting the risk did not increase until about 18 months after patients first started taking Vioxx.

Dr Harlan Krumholz, a Yale University cardiologist who has assisted Vioxx plaintiffs suing Merck, told the Associated Press the study was a “red flag”.

“It adds another important chapter to the Vioxx story, but also an important warning to us about how we assess the safety of medication.”

In response to the study, Merck released a statement saying: “Merck believes that this post-hoc analysis using limited data from a prematurely terminated study needs to be interpreted very cautiously and in the context of the rest of the data from the extensive clinical development programme for Vioxx.”

At the time Vioxx was withdrawn from the market, it had been generating $2 billion in annual sales.