Millions of people who take aspirin to prevent a heart attack may need to rethink their pill-popping, Harvard researchers reported Monday.
A daily low-dose aspirin is recommended for people who have already had a heart attack or stroke and for those diagnosed with heart disease.
But for the otherwise healthy, that advice has been overturned.
Guidelines released this year ruled out routine aspirin use for many older adults who don't already have heart disease — and said it's only for certain younger people under doctor's orders.
Some 29 million people 40 and older were taking an aspirin a day despite having no known heart disease in 2017, the latest data available, according to a new study from Harvard and Beth Israel Deaconess Medical Center. About 6.6 million of them were doing so on their own — a doctor never recommended it.
And nearly half of people over 70 who don't have heart disease — estimated at about 10 million — were taking daily aspirin for prevention, the researchers reported in Annals of Internal Medicine.
"Aspirin can marginally help people who don't have heart disease," explained Dr. Michael Lesko, System Director of Preventative Cardiology, Geisinger Medical Center, in Danville. "But the risks outweigh the benefits. For someone who has had a heart attack, the benefits outweigh the risk."
Aspirin is a blood thinner, and some of the risks of taking unneeded doses include clot-related stroke, a bleeding stroke, or gastrointestinal bleeding, Lesko said.
In the 1980s, Lesko noted, "there was a huge study," and doctors urged people to leverage aspirin's blood-thinning properties to lower the chances of a first heart attack or stroke.
Then last year, three surprising new studies challenged that dogma. Those studies were some of the largest and longest to test aspirin in people at low- and moderate-risk of a heart attack, and found only minimal benefit if any, especially for older adults. Yet the aspirin users experienced markedly more digestive-tract bleeding, along with other side effects.
"Many patients are confused about this," said Dr. Colin O'Brien, a senior internal medicine resident at Beth Israel, who led the study.
In March, those findings prompted a change in American Heart Association and American College of Cardiology guidelines:
— People over 70 who don't have heart disease — or are younger but at increased risk of bleeding — should avoid daily aspirin for prevention.
— Only certain 40- to 70-year-olds who don't already have heart disease are at high enough risk to warrant 75 to 100 milligrams of aspirin daily, and that's for a doctor to decide.
Nothing has changed for heart attack survivors: Aspirin still is recommended for them.
But there's no way to know how many otherwise healthy people got the word about the changed recommendations.
"We hope," O'Brien said, "that more primary care doctors will talk to their patients about aspirin use, and more patients will raise this with their doctors."
The Associated Press Health and Science Department contributed to this story.