Blood Thinners for Heart Disease - Aspirin

What is aspirin?

Aspirin is an antiplatelet medication. Antiplatelets make the blood less sticky, which helps prevent blood clots from forming.

Can aspirin help during a heart attack?

Studies show that taking aspirin during a heart attack reduces the risk of dying by 23%.¹¹ A chewed aspirin (162-325 mg) helps prevent further clots developing. Research shows that women having a heart attack are just as likely to benefit from aspirin as men.¹²

Can aspirin prevent another heart attack in women who've already had one?

Women who have already had a heart attack, stroke, or undergone angioplasty or bypass surgery should take daily aspirin (75-325 mg).7, ¹³ Aspirin reduces the chances of further heart problems by 25%.¹⁴ Although aspirin sometimes works as a painkiller, it does not reduce chest pain ( angina). It does reduce the risk of dying for people who suffer from angina.¹⁵ One small study suggested that aspirin may not be as effective in women with angina compared with men. The women taking aspirin were more likely to suffer episodes of chest pain than men.¹⁶

If I'm at risk for heart disease, should I take aspirin?

What about women who have not had a heart attack or stroke — should they take a daily aspirin? The most recent guidelines for the prevention of cardiovascular disease in women recommend daily aspirin (75-162 mg) for women at high-risk for coronary artery disease.¹⁷ High risk is defined as a greater than 20% risk of developing heart disease within 10 years. Women at intermediate risk (10% to 20% 10-year risk) may also take aspirin provided their blood pressure is under control. To find out if you meet the “at risk” criteria, use this risk calculator. People with type 2 diabetes have a high risk of developing heart disease and may be told to take daily aspirin.

Should women at low risk for heart disease take aspirin?

Because many of the early prevention studies on aspirin did not include women, an expert panel noted that the benefits are less established for healthy middle-aged women than for men.¹⁸ To address this gap, the Women's Health Study enrolled approximately 40,000 healthy women 45 years of age or older and gave them 100 mg of aspirin or a dummy pill to take every other day.¹⁹ After 10 years, there was no difference in the risk of having a heart attack or dying from cardiovascular disease between the two groups. This is in contrast to the benefits seen for healthy men in previous studies. The results did not differ whether women were menopausal or taking hormones, but older age did have an effect. Women taking aspirin who were older than 65 years at the beginning of the study experienced a 34% reduction in the risk of having a heart attack.

Does aspirin prevent stroke?

The Women's Health Study did show that aspirin could prevent stroke, a benefit that has not been shown in men. Women taking aspirin were 24% less likely to suffer ischemic stroke, the most common type of stroke caused by a blood clot in an artery of the brain.19 Because aspirin thins the blood, there was a slight increase in the risk of hemorrhagic stroke or bleeding in the brain; however, this was not statistically significant, and overall aspirin reduced the risk of any stroke by 17%.

How does aspirin work differently in men and women?

Since the Women's Health Study had different results to previous studies in men, researchers decided to further investigate the gender differences. They pooled the results of six studies on aspirin involving almost 95,500 people (more than half were women) who did not already have heart disease, but who may have had risk factors. The results showed that in women aspirin reduced the risk of any stroke by 17%, but did not lower the risk of heart attack.²⁰ Men taking aspirin saw a 32% reduction in heart attack risk, but no stroke benefit.

Aspirin reduced women's risk of the most common type of stroke (ischemic) risk by 24%. For hemorrhagic stoke (one caused by a burst blood vessel in the brain), aspirin had no effect on a women's risk. However, aspirin increased a man's risk of hemorrhagic stroke by 69%. The researchers believe the sex difference may have several explanations. First, women experience more strokes than heart attacks, while men experience more heart attacks than strokes. Second, men and women process aspirin differently; women are more likely to experience aspirin resistance, in which a person's blood does not thin in response to the aspirin.

What is the best daily dose?

Despite the wealth of research supporting the use of daily aspirin in people at risk for heart disease, it's not clear what dose is best. This is because the studies conducted so far have used a wide variety of doses. It has been shown that higher doses (500 mg to 1.5g) are no better at preventing platelets from sticking than doses in the range of 75 to 325 mg.¹⁴ The research also suggests that baby aspirin (81 mg) is as effective as higher doses. Lower doses are generally preferred because they are less likely to trigger serious side effects such as bleeding in the stomach. However, low doses may still cause gastric side effects including nausea.²¹ If your physician prescribes daily aspirin, you can discuss which dose works best for you.

What are the risks of aspirin use?

Regular aspirin is associated with serious side effects, particularly bleeding in the stomach. The risk of this side effect is higher for people older than 70 years of age. There was a 40% increase in the risk of serious gastrointestinal bleeding requiring a blood transfusion in women taking aspirin in the Women's Health Study.¹⁹ These women were also more likely to experience minor bleeding and bruising.

More common side effects include upset stomach and nausea. In a study conducted among male physicians, nearly 40% of the doctors assigned aspirin stopped taking it because of gastrointestinal problems (they were taking 325 mg every other day).²² Enteric and buffered-coated aspirin preparations are touted as easier on the stomach but there is research suggesting they are not any safer.²³ Taking regular aspirin reduces the risk of the most common type of stroke, ischemic stroke (when a blood clot lodges in a blood vessel in the brain). Conversely, aspirin slightly increases the risk of hemorrhagic stroke²⁴ (bleeding in the brain) although this may be less of an issue in women than in men.²⁰

You should not take daily aspirin (or most other painkillers) if you drink more than 3 alcoholic drinks per day. This combination increases your risk of liver damage and bleeding in the stomach.¹³ If you are taking a nonsteroidal anti-inflammatory drug (NSAID, e.g., Aleve) regularly, to treat arthritis pain for example, you should not take daily aspirin. The risks of serious side effects and even death increase when daily aspirin is combined with regular NSAID use.²⁵ Taking an occasional NSAID is fine. If you are prescribed daily aspirin to prevent a heart attack, you should avoid ibuprofen (Advil, Motrin) because it interferes with the cardioprotective effects of aspirin.⁷

Do the benefits of aspirin outweigh the risks?

In people at high risk for heart disease, the benefits of daily aspirin far outweigh the risks. That is not the case for men and women at low-risk, which is why daily aspirin is not recommended for everyone and why you should not start taking it without discussing the risks with your healthcare provider. Healthy women who are at low-risk for heart disease should not take aspirin because the risks far outweigh any benefits.

Are some people resistant to aspirin?

Aspirin protects the heart by making the blood less likely to clot. However, laboratory tests have shown that aspirin doesn't work in some people. These people are deemed aspirin-resistant. One study found that among men and women taking aspirin, those who tested as aspirin-resistant were more than 3 times as likely to have a heart attack, stroke, or die than non–aspirin-resistant patients.²⁶ There was suggestive but not conclusive evidence that women were more likely than men to be aspirin-resistant. Blood and urine tests for aspirin-resistance are not routinely available, but there are a few in development.

Are women missing out on aspirin?

Research shows that the number of women taking aspirin has increased greatly in recent years. A study of more than 25,000 people with coronary artery disease found that 81% were taking aspirin in 1999 compared with only 59% in 1995.²⁷ Even so, women were less likely than men to be taking aspirin. An analysis of nearly 3,000 postmenopausal women with heart disease found that those at the greatest risk for a heart attack or stroke were the least likely to be taking aspirin suggesting that there is still room for improvement.²⁸

On the contrary, there is evidence showing that some healthy women may be taking aspirin inappropriately. An analysis from the Minnesota Heart Survey, which includes more than 20,000 people (more than half are women), found that 31% of women at low-risk for heart disease were taking daily aspirin even though it's more likely to cause harm in people at low-risk.²⁹

Aspirin Quick Reference Table