Research shows that taking an aspirin a day can help prevent a stroke or a heart attack only in some people, not everyone. This practice can also lead to adverse side effects.

The Food and Drug Administration probed the merit of taking an aspirin to help avoid a stroke or heart attack in people who never had previous cardiovascular problems. FDA also rejected German drugmaker Bayer-Healthcare's request to change its labeling packages to market aspirin as a primary prevention indication.

For decades, medical data showed that a low dose of aspirin a day can help prevent a stroke or heart attack from reoccurring. An aspirin dose ranges from 80 mg. to a 325 mg. tablet. This is called "secondary prevention."

However, FDA carefully examined the data from major researches and concluded that an aspirin a day does not prove to be beneficial to people who haven't had a stroke, heart attack or any cardiovascular problem. FDA said the data do not support this practice as a primary prevention and in addition, it can even cause risks including dangerous bleeding into the stomach or brain.

The American Heart Association (AHA) and other health organizations support taking an aspirin a day for people who have a high risk of heart attacks. It recommends that these people take a low dose of aspirin daily if advised by their physician.

People who have a heart attack developed a clot in one of their coronary arteries which supply blood to the heart. This clot obstructs the oxygen and blood flow to the heart. Aspirin is said to interfere with the blood's clotting action. However, FDA emphasizes that data is not enough to prove aspirin's benefit in people who are at an increased risk. Patients should also take extra precaution when using aspirin while taking other blood thinners including dabigatran (Pradaxa), warfarin, apixiban (Eliquis) and rivaroxaban (Xarelto).

"Today's ruling does not impact the numerous cardiovascular indications for which aspirin is already approved," Bayer spokesperson Chris Loder said. "It is critical that patients who are already on aspirin therapy remain so. No one should stop or modify their aspirin regimen without first consulting with a healthcare provider. For those already on aspirin therapy, suddenly stopping can be dangerous."

There are other major studies which continue to examine the use of aspirin as a primary prevention of stroke and heart attack and FDA still monitors these studies.