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 flip side, 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
St Joseph (McNeil Consumer)
How it is given:
What it is used for:
To reduce the risk of death or ischemic stroke in people who already had an ischemic stroke (blood clot in the brain) or transient ischemic attack (TIA or mini stroke)
You should not be treated with it if:
You should not take aspirin in the last 3 months of pregnancy unless your physician has told you it is safe; aspirin is excreted in breast milk.