The two popular painkillers Vioxx and Celebrex, heavily marketed as "super-aspirin," were prescribed for millions of patients who did not need them or should not have taken them, researchers said.

Merck & Co. Inc's Vioxx was recalled in September because a study linked the drug to increased risk of heart attacks and strokes, while Pfizer's Celebrex is under a cloud after data showing a similar heightened risk.

The study by doctors at Stanford University and the University of Chicago found the two COX-2 inhibitors were taken by millions of people who were not at risk of gastrointestinal bleeding, the main reason patients were told to switch from aspirin and other lower-cost painkillers.

COX-2 inhibitors cost 10 to 15 times as much as the drugs they replaced, the study published in the Archives of Internal Medicine said.

"We found a rapid, nationwide shift away from older, inexpensive drugs with better established safety and efficacy to newer, costly drugs with no real history," said study author G. Caleb Alexander, a medical ethicist at the University of Chicago.

Within a year of being introduced in 1999, Vioxx and Celebrex were being heavily promoted as "super-aspirin" and bringing in billions of dollars in revenue annually, the study said. Merck spent $161 million in 2000 on direct-to-consumer marketing of Vioxx, it said.

Using data from the National Center for Health Statistics, the study concluded that 73 percent of patients considered at low or very low risk of gastrointestinal problems should not have been considered for the newer drugs. Gastrointestinal bleeding usually affects only at-risk patients who must take aspirin and other non-steroidal anti-inflammatory drugs, or NSAIDs, for long periods, it said.

By 2002, 17.6 million patients at low risk of gastrointestinal bleeding, or 66 percent of those patients, were taking one of the two COX-2 inhibitors, the study said.

The drugs were also taken by millions of people who should not have been, including 16 million people suffering from congestive heart failure, or liver or kidney dysfunction. These patients might also have been hurt by NSAIDs, it said.

"The findings demonstrate the challenge of limiting innovative therapies to the settings in which they are initially targeted and maximally cost-effective," Alexander wrote.

The U.S. Food and Drug Administration is convening a panel next month to examine the COX-2 inhibitors, including Pfizer's new entry Bextra, which has also been found to raise the risk of heart attack in people who have had heart bypass surgery.

Spokesmen for Pfizer and Merck could not immediately comment.