Can an aspirin a day help you ward off a heart attack or stroke?

That depends.

Scientific evidence shows that taking an aspirin daily can help prevent a heart attack or stroke in some people, but not in everyone. It also can cause unwanted side effects.

According to Robert Temple, M.D., deputy director for clinical science at the Food and Drug Administration (FDA), one thing is certain: You should use daily aspirin therapy only after first talking to your health care professional, who can weigh the benefits and risks.

Who Can Benefit?

"Since the 1990s, clinical data have shown that in people who have experienced a heart attack, stroke or who have a disease of the blood vessels in the heart, a daily low dose of aspirin can help prevent a reoccurrence," Temple says. (A dose ranges from the 80 milligrams (mg) in a low-dose tablet to the 325 mg in a regular strength tablet.) This use is known as "secondary prevention."

However, after carefully examining scientific data from major studies, FDA has concluded that the data do not support the use of aspirin as a preventive medication by people who have not had a heart attack, stroke or cardiovascular problems, a use that is called "primary prevention." In such people, the benefit has not been established but risks—such as dangerous bleeding into the brain or stomach—are still present.

Caution Needed With Other Blood Thinners

When you have a heart attack, it's because one of the coronary arteries (which provide blood to the heart), has developed a clot that obstructs the flow of blood and oxygen to the heart. Aspirin works by interfering with your blood's clotting action.

Care is needed when using aspirin with other blood thinners, such as warfarin, dabigatran (Pradaxa), rivaroxaban (Xarelto) and apixiban (Eliquis).

What about people who have not had heart problems or a stroke but who, due to family history or showing other evidence of arterial disease are at increased risk? Is an aspirin a day a safe and effective strategy for them?

Again, Temple emphasizes, the clinical data do not show that a benefit in such people.

He adds, however, that there are a number of ongoing, large-scale clinical studies continuing to investigate the use of aspirin in primary prevention of heart attack or stroke. FDA is monitoring these studies and will continue to examine the evidence as it emerges.

In the Meantime

The bottom line is that in people who have had a heart attack, stroke or cardiovascular problems, daily aspirin therapy is worth considering. And if you're thinking of using aspirin therapy, you should first talk to your health care professional to get an informed opinion, Temple says.

Finally, how much aspirin you take matters. It's important to your health and safety that the dose you use and how often you take it is right for you. Your health care professional can tell you the dose and frequency that will provide the greatest benefit with the least side effects.

If your health care professional recommends daily aspirin to lower the risk of a heart attack and clot-related stroke, read the labels carefully to make sure you have the right product. Some drugs combine aspirin with other pain relievers or other ingredients, and should not be used for long-term aspirin therapy.

This article appears on FDA's Consumer Updates page, which features the latest on all FDA-regulated products.