Daily aspirin therapy won’t prevent a first heart attack or stroke and may increase the risk of fatal stomach bleeding. That’s the conclusion of a large new review of the risks and benefits of low dose aspirin therapy.

A small dose of aspirin daily has long been recommended to ward off a second episode of cardiovascular disease. This is called secondary prevention, and researchers stress that this is still helpful. 

“The evidence that aspirin will help prevent another heart attack is overwhelming, convincing and isn’t seriously challenged. So for [these patients], if they are taking aspirin, we are not offering them any new news. We are saying yes, according to the evidence you are doing the right thing,” says Ike Iheanacho, MD, editor of the Drug and Therapeutics Bulletin, a publication produced by an independent group in Britain that examines existing research and expert opinion.

But increasingly, doctors have been recommending low-dose aspirin to their patients for primary prevention of cardiovascular disease, and experts say that in those cases, the benefits are less clear-cut. 

After analyzing six controlled studies on the topic involving 95,000 patients, the Drug and Therapeutics Bulletin is now suggesting that the guidelines about aspirin be amended for patients who’ve never had heart trouble because they say aspirin doesn’t prevent cardiovascular deaths in this group and may cause serious internal bleeding.

Dr. Iheanacho says the latest evidence shows if you take 2,000 patients and treat them for a year with a daily aspirin, you’ll only prevent one heart attack. And he says that for every 3,300 people you treated for a year, you’d get one extra incident of gastrointestinal bleeding, which can be fatal.

 “Yes, you can say it’s a very small risk. But you can also say a lot of people are taking aspirin and it won’t make a big difference to preventing a heart attack or stroke,” he explains.

There has not been a study on the effect of a daily low dose aspirin on people with inflammatory arthritis, which can bring with it a nearly doubled risk of heart disease. But there have been studies on people with diabetes, who are also considered a high-risk group, and they show no benefit to a daily aspirin.

“The evidence doesn’t show so far that the prediction of high risk – whether family history or another condition – in itself, that doesn’t seem to be a predictor of who will benefit from aspirin and who won't,” Dr. Iheanacho says.

Eric Bates, MD, a cardiologist at the University of Michigan Health System in Ann Arbor, says he believes this new recommendation is likely correct. 

He says the previous encouragement to take an aspirin a day was in an era before statin therapy, blood pressure control, diabetes control and other methods existed to help decrease risk. “The risk benefit balance has probably changed between the old era where we didn’t do a good job with prevention and risk factor control versus the new era,” Dr. Bates says.

Jon Giles, MD, works in the Johns Hopkins Arthritis Center and is an assistant Professor of Medicine at the institution in Baltimore. He agrees with the message that a daily aspirin doesn’t help and could actually hurt patients – especially those with rheumatoid arthritis, or RA.

“The adverse consequences of aspirin, both gastrointestinal and intracranial bleeding, are increased in RA patients because the majority also use nonsteroid anti-inflammatory drugs, or NSAIDs, daily or frequently, and many also use prednisone, which together increase the GI bleeding risk. Thus, any beneficial effect in cardiovascular disease prevention could completely be wiped out or exceeded by bleeding risk,” Dr. Giles explains.

The Drug and Therapeutics Bulletin is now calling on doctors to review the cases of patients currently taking a daily aspirin to prevent heart disease.

“I wouldn’t say to any patient – stop taking it. Those are individual decisions,” Dr. Iheanacho says. “If someone has inflammatory arthritis and they’ve seen several of their family members die from it, it may well be an overriding priority to take any measures which they think might help them have not such an episode. And that seems like an entirely reasonable way of proceeding. The only qualm of mine is that should be an informed choice. People should be allowed to know what the latest evidence is and be helped to make a judgment about how that relates to their particular situation. In our view, we think there’s not enough evidence to recommend using it, but we recognize that will be an individual decision.”