NEW YORK (CNNMoney.com) -- The New England Journal of Medicine posted a correction in its current issue, removing its previously published finding that it takes at least 18 months for heart attack risks to increase from use of Vioxx, the anti-arthritis painkiller that Merck pulled from the market.

The correction could be used as a legal weapon against Merck (up $0.34 to $35.28, Charts), the drugmaker that withdrew Vioxx, a former blockbuster, in 2004 as a result of this "Approve" study. Since then, more than 10,000 lawsuits have been filed against the drugmaker from former Vioxx patients and their families, blaming the drug for causing heart attacks.

The original finding, that risks emerged only after 18 months of Vioxx use, has been used by Merck's lawyers as an important part of its defense. The NEJM finding could undermine that strategy.

The NEJM correction stems from an announcement that Merck made May 30. Merck said it was correcting its "prior description of one of the statistical methods used in the Approve study."

On Monday, Merck stood by its original results for the Approve study, acknowledging a heightened risk of heart attacks after 18 months of Vioxx use, but not before.

"As we have said previously and affirm today, this correction did not change the data in the Approve study or its results," said Peter Kim, president of Merck Research Laboratories, in a press release.

Merck was preparing to respond to the publication of the correction.

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