NEW YORK (CNNMoney.com) - Merck announced that Vioxx patients did not suffer an increased risk of heart attacks from blood clots after they stopped taking the drug, though the company said it would not change its legal strategy regarding the withdrawn painkiller.

Merck (down $0.16 to $34.51, Research) withdrew Vioxx, an arthritis painkiller, on Sept. 30, 2004 after its Approve study showed an increased risk of heart attacks and strokes from blood clots in patients who took the drug for at least 18 months. More than 11,500 lawsuits have been filed against the company since that time.

But Merck said on Thursday that further analysis of the Approve study showed that patients did not have an increased risk of blood clot-related heart attacks after they stopped taking the drug. This follow-up "off-drug" study was conducted in patients for one year, following three years of taking the drug.

Peter Kim, president of Merck Research Laboratories, said, in a teleconference on Thursday, that there was "no statistical difference" in heart attack risks related to blood clots or thrombosis in the off-drug phase of the study.

Merck general counsel and senior vice president Ken Frazier said the company would continue to defend itself one case at a time, and denied allegations that Merck acted improperly.

"We will continue to defend these cases on the scientific facts of causation, as well as the responsibility of the company's actions," said Frazier. "The follow-up data from Approve does not change our litigation strategy at all."

So far, Merck has lost two cases, won two, and had a split verdict in another.

Merck said that other studies of Vioxx have not shown an increased risk of heart attacks or stroke.

To read about the most recent Vioxx verdict, click here.

To read about an independent Canadian study about Vioxx, click here.

To read about Merck's Fosamax lawsuits, click here.