If you've never had a heart attack or stroke, you likely should not be taking aspirin to prevent them, according to new research.

"This is the most significant practice-changing evidence to come out in the past year," said Michael Kolber, a family medicine professor at the University of Alberta and co-author of a paper published in Canadian Family Physician, along with recent University of Calgary family medicine graduate Paul Fritsch.

Kolber and Fritsch reviewed three large, randomized, placebo-controlled studies published in 2018 that showed the risk of major internal bleeding associated with taking an aspirin a day is higher than any preventative benefits.

"These aren't nosebleeds or bleeding gums," Fritsch said. "These are major internal bleeds where the patients need hospitalization and perhaps a blood transfusion, so they're of major clinical, and also personal, significance."

Fritsch said one of the studies also showed an increase in deaths from all causes, and in particular cancer deaths, among the patients who took aspirin, which is also called acetylsalicylic acid or ASA.

The advice to take a daily aspirin to prevent heart disease became dogma in the 1990s but it was based on flawed research, according to Kolber.

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In an earlier study, Kolber found that 40 per cent of Albertans over the age of 50 take aspirin to prevent cardiovascular disease, even though most have never had a cardiovascular event. He noted that aspirin is still considered beneficial for those who do have heart disease.

"We really see an aspirin gap," said Kolber. "There are a lot of people taking aspirin for primary prevention who don't need it, and there's a group of people who already have cardiovascular disease who aren't taking it, and they should be."

Kolber advises those who have never had a heart problem to use other preventive measures.

"Instead of just taking a daily aspirin like we've been taught for a generation, we would recommend patients stop smoking, exercise, track their blood pressure and consider the Mediterranean diet."

Kolber said people with elevated future cardiovascular risk might consider taking a statin, which lowers cholesterol.

"The evidence for those measures is far superior to the evidence for aspirin," he said.

Kolber and Fritsch's findings were distributed electronically through Tools for Practice, evidence summaries compiled by the U of A's evidence-based medicine team, PEER (Patients, Experience, Evidence, Research). They are read by 40,000 health-care professionals around the world and funded by the Alberta College of Family Physicians and the Canadian College of Family Physicians.