While taking an aspirin daily has been proven to lower your risk of heart attack, it may not help prevent a stroke.

A recent global study involving more than 12,500 patients who exhibited several cardiovascular risk factors (smoking, high blood pressure, etc.) shows that taking an aspirin daily reduced the risk of heart attack by a whopping 82 percent. However, there was no decrease in risk of suffering a stroke.

"Participants who took aspirin tended to have fewer heart attacks, particularly those aged 50-59 years, but there was no effect on stroke," said professor J. Michael Gaziano, principal investigator of the Brigham and Women's Hospital in Boston. "As expected, rates of gastrointestinal bleeding and some other minor bleedings were higher in the aspirin group, but there was no difference in fatal bleeding events between groups."

However for those who don't have risk factors, you may want to avoid aspirin altogether.

Several studies released in September 2018 showed that taking a low-dose aspirin daily provided no significant health benefits.

In one study, nearly 10,000 participants were given an aspirin everyday for five years and another 10,000 people were given a placebo. At the end of the five-year study, researchers noted the only major difference was more people in the aspirin group suffered overall bleeding.

The second study further supports that finding. "The use of low-dose aspirin as a primary prevention strategy in older adults resulted in a significantly higher risk of major hemorrhage and did not result in a significantly lower risk of cardiovascular disease than placebo," the study's authors wrote.

Not only can taking a daily aspirin cause hemorrhaging, it can also increase your risk of dying at a younger age according to the third study. Researchers found that "higher all-cause mortality was observed among apparently healthy older adults who received daily aspirin than among those who received placebo and was attributed primarily to cancer-related death."

More harmful for women than men

These findings aren't completely shocking though. For years, the research has been out that a daily regimen of aspirin may do more harm than good.

In a 2015 study published in the Journal of the American College of Cardiology, researchers from Baylor College of Medicine in Texas found that nearly 12 percent of patients who had been prescribed aspirin should not be taking the medicine. And because aspirin is available over-the-counter, the team suggests this number may be even higher when considering the number of patients who have self-prescribed a daily dose. Aspirin helps to thin the blood and can be used to prevent blood clots, but researchers believe that for many patients, an aspirin a day could do more harm than good.

Researchers looked at the medical records for 68,000 patients and calculated each one's risk for developing heart disease or having a stroke over the next decade. They considered factors such as age, gender and blood pressure. Researchers excluded patients with a history of cardiovascular disease, since previous studies clearly show that a daily dose of aspirin can help prevent heart attacks in this group. But they found that there were a number of low-risk patients taking aspirin who probably shouldn't be.

The team found that inappropriate use of aspirin occurred more frequently in women — around 17 percent — than in men, where it was closer to 5 percent. In these cases, researchers concluded that their risk for heart disease and stroke was not great enough to warrant a daily dose of aspirin. And previous studies have shown that the risks of aspirin therapy could outweigh the benefits, particularly in women.

In one study, published in the journal Heart, 28,000 healthy women age 45 and older, were given either a placebo or 100 milligrams of aspirin every other day. After 15 years, researchers noted that the daily aspirin use reduced the risk for cardiovascular disease by a small amount; however, a large number of the women in the study suffered from long-term gastrointestinal bleeding.

Weight is a key factor

A person's weight can also determine the effectiveness of aspirin for preventing cardiovascular events. A new study in The Lancet shows the majority of people who took a low-dose aspirin daily and weighed more than 154 pounds gained no benefit from the medicine compared to people who weighed less. Researchers concluded that a "one-size-fits-all" approach to taking aspirin isn't the best method for preventing cardiovascular issues such as heart attack or stroke.

Bottom line: For those whose risk of heart attack and stroke is low, the risk of developing complications from daily aspirin use may be too great. Talk to your doctor about if you should (or shouldn't) be taking a daily dose of aspirin.

Editor's note: This article has been updated since it was originally published in January 2015.

Who really needs a daily dose of aspirin?
Researchers find that more than 10 percent of patients may be taking aspirin unnecessarily, and the risks may outweigh the benefits.