Blood Thinners & Aspirin - Aspirin

What is aspirin?

Aspirin is an antiplatelet medication that stops blood clots from forming by preventing small blood cells (platelets) from sticking to each other and clumping. It is the most widely used medication to prevent blocked-vessel (ischemic) stroke and heart disease. Aspirin (160 to 325 mg) can also be used during the emergency treatment of stroke if you are not eligible for tPA, the first-choice treatment.^{1, 2}

Who should take daily aspirin to prevent stroke?

Women at high risk for stroke may benefit from taking a daily aspirin to prevent a first blocked-vessel (ischemic) stroke.^{3, 4} You are considered at high risk for stroke if you have:

• Heart disease
• Diseases of the blood vessels in the head or neck ( carotid artery disease)
• Poor circulation in the legs, arms, stomach, and kidneys
• An aneurysm in the aorta, the large artery leaving your heart
• Kidney disease
• Diabetes
• A greater than 20% chance of heart attack or stroke in the next 10 years. Click here to calculate your risk.

Women at intermediate risk for stroke and any woman older than 65 with their blood pressure under control should consider regular aspirin (81 mg daily or 100 mg every other day) to prevent stroke.^{4, 10} In these women, the increased bleeding risks can sometimes outweigh the reduction in stroke risk, so you should talk to your doctor to see if daily aspirin is the right choice for you.^{4, 10} You are considered to be at intermediate risk for stroke if you have:

• 10% to 20% risk of heart attack or stroke in the next 10 years. Click here to calculate your risk.
• One or more of these risk factors: smoking, poor diet, physical inactivity, obesity, family history, hypertension

Women younger than 65 at high risk of stroke benefit from the stroke-preventing properties of aspirin. It is not clear if women younger than 65 who are at low risk for stroke benefit from taking aspirin. The Women's Health Study examined low-dose aspirin (100 mg) taken every other day by healthy women older than 45 years, and found no significant reduction in the risk of blocked-vessel (ischemic) stroke in women younger than 65. The study also found that women taking the aspirin had an 18% increase in stomach bleeding compared with the women taking a dummy pill, and were slightly more likely to need a blood transfusion.¹⁰

Should I take aspirin if I've already had a stroke?

Women who have a blocked-vessel (ischemic) stroke and who are not eligible for the first-choice treatment with tPA should receive aspirin (within 24 to 48 hours of when symptoms first appeared) to reduce the chances of dying or suffering another stroke.^{1, 2}

For women who have already had a stroke or TIA, taking regular aspirin in the long-term is one effective option for preventing another stroke. The combination of aspirin and extended-release dipyridamole is now recommended over aspirin alone.¹¹ A safe alternative to aspirin alone for the prevention of stroke is clopidogrel.⁵ Aspirin in addition to clopidogrel, however, has been shown to increase the chances of bleeding and is not recommended for people who have had a stroke or TIA, unless they have had a stent implanted in a blood vessel or have acute coronary syndrome.^{11, 12} These options carry different levels of bleeding risk, so discuss the risks and benefits of each preventive therapy with your doctor if you've had a stroke.

Aspirin can also be used to prevent blood clots and future strokes in women who had a stroke and have atrial fibrillation but can't take an oral anticoagulant like warfarin (Coumadin).⁵ If you have replacement heart valves, or if you are confined to bed after a stroke and doctors are worried about clots forming in the veins of your legs or in your lungs, you may receive aspirin in addition to warfarin.

Pregnant women with lower risks of developing blood clots may be treated with standard or low-molecular-weight heparin in the first trimester, followed by low-dose aspirin for the rest of the pregnancy.⁵

Who should not take aspirin?

Unlike during a heart attack, you should not immediately take aspirin if you think you're having a stroke; taking aspirin during a bleeding (hemorrhagic) stroke could make it worse. See "How to Survive a Stroke."

While many women may benefit from taking aspirin regularly to prevent stroke, in some women the increased bleeding risks may outweigh the benefits. Never start an aspirin regimen to prevent stroke without first discussing it with your doctor. If you have high blood pressure you should not take aspirin until your blood pressure is under control. If you are taking birth control pills, or have had an allergic reaction or developed resistance to aspirin in the past, ask your doctor if it's safe for you to take aspirin.

What is the best aspirin dose?

To prevent a first stroke, guidelines recommend that women at high risk take aspirin in doses ranging from 75 to 325 mg per day.^{3, 4} Women at intermediate risk and women older than 65 who are taking aspirin to prevent stroke should take either 81 mg each day (a baby aspirin) or 100 mg every other day.^{4, 10} You should work with your doctor to determine the aspirin dose that is best suited to you. In the US, most doctors (about 60%) prescribe 81 mg a day, and 35% prescribe 325 mg a day, since these doses are commonly available over the counter.¹³

What are the risks of aspirin?

Because aspirin interferes with the blood's ability to clot, there is a slight increase in the risk of bleeding (hemorrhagic) stroke and bleeding in the stomach, which is more common with higher doses of aspirin. Bleeding in the stomach is associated with a slightly higher chance of needing a blood transfusion.¹⁰ You should try to take the lowest possible effective dose for preventing stroke: there is no evidence that high doses prevent more strokes than low doses.

Other side effects of aspirin may include upset stomach, nausea, easy bruising, blood in the urine, and nose bleeds.¹⁰ Buffered or coated aspirin may be easier on the stomach. However, there is no evidence that they are safer.

Aspirin Quick Reference Table

Next: Clopidogrel