The widely prescribed diabetes drug Avandia is linked to a greater risk of heart attack and possibly death, suggests a new scientific analysis published online Monday.

More than six million people worldwide, including patients in Canada, have taken the drug sold by London-based GlaxoSmithKline PLC since it came on the market eight years ago. Pooled results of dozens of studies revealed a 43 per cent higher risk of heart attack, according to the review published by the New England Journal of Medicine.

Experts said the overall risk was small and cautioned people not to stop taking the drug on their own but to talk to their doctors.

The company downplayed the report of heart risks, saying the analysis by Dr. Steven Nissen and statistician Kathy Wolski at the Cleveland Clinic is not definitive scientific proof.

In a conference call Monday, Dr. Lawson McCartney, who leads Glaxo's diabetes drug development, said the company is not seeing "anything like" the problems reported in the medical journal.

"We remain very confident in the safety and of course in the efficacy of Avandia as an important diabetic medicine," McCartney said.

The government will take no immediate action on a label change or other measures regarding the drug, said Dr. Robert J. Meyer of the U.S. Food and Drug Administration's Center for Drug Evaluation and Research.

Health Canada said it will analyze the results of the latest study and others as part of its assessment of the drug's risks and benefits. There are no immediate plans to change the labelling for Avandia, the department said in an e-mail to CBC News on Tuesday.

FDA officials acknowledged that Glaxo submitted information last August indicating some increased risk from the drug but that other studies were contradictory.

A U.S. House committee will hold a hearing into the FDA's oversight of the safety of the drug, Rep. Henry Waxman said Monday. He chairs the House Oversight and Government Reform Committee.

Avandia is used to treat Type 2 diabetes, the most common form of the disease, which is linked to obesity and afflicts 18 million Americans and 200 million people worldwide. This form of diabetes occurs when the body does not make enough insulin or cannot effectively use what it manages to produce.

Avandia helps sensitize the body to insulin and was considered a breakthrough medication for blood-sugar control. In 2006, Canadian retail pharmacies dispensed more than 14,289,000 prescriptions for Avandia, IMS Health Canada estimated.

Talk about concerns with doctors

Worried patients should not quit Avandia on their own and should discuss concerns with their doctors, wrote Drs. Bruce Psaty and Curt Furberg in an editorial in the New England Journal. Psaty is with the University of Washington in Seattle and Furberg is with Wake Forest University.

The advice, which the FDA backed in a safety alert, holds for Canadians as well, agreed internist Dr. Sonia Anand of McMaster University in Hamilton.

However, to the extent that the new analysis shows valid risks, the drug "represents a major failure of the drug-use and drug-approval processes in the United States," Psaty and Furberg  said.

When the drug was approved, "evidence was at best mixed" on its benefit, wrote the two doctors.

Both have been frequent critics of the FDA's failure to spot dangers in the drug approval process and its conduct in the case involving Vioxx. The popular arthritis medicine sold by Merck & Co. was taken off the market in 2004 when heart problems came to light after it had been taken by millions of people.

There may be a silver lining to the drug findings.

"I think we've pretty much abandoned the whole diet, exercise approach, and I think this should refocus us on diet and exercise," said diabetes researcher Dr. Jay Woortman of West Vancouver.