Low-Dose Aspirin Therapy

Topic Overview

Why take low-dose aspirin?

Good old aspirin, the common pain reliever that has been in our medicine cabinets for almost a century, also has a talent for prevention. Aspirin can help prevent a heart attack or a stroke in people who have never had a heart attack or stroke. Aspirin has been proved to prevent a first and second heart attack in people who have coronary artery disease.1 It also reduces the risk of having a stroke in those who have had a previous stroke or a transient ischemic attack (a temporary interruption of blood flow to the brain), which is often a warning sign of an impending stroke.2 When taken during and after a heart attack, aspirin can reduce your chances of dying.3

Who should take low-dose aspirin?

It has been well documented that aspirin reduces the risk of heart attack in people with known coronary artery disease (CAD). It is also now understood that aspirin lowers the risk of having symptoms for people who have a higher risk for the disease. People who are at high risk for coronary artery disease or who already have coronary artery disease benefit the most from aspirin therapy.

You can take aspirin to help you during a heart attack. After you call 911 or other emergency services, chew 1 adult-strength (325 mg) or 2 to 4 low-dose (81 mg) aspirin if you are not allergic to aspirin and if there is no other reason that you can't take aspirin. Aspirin slows blood clotting, so a blood clot that is causing the heart attack stays smaller.

You may also take low-dose aspirin (81 mg) every day to help lower the risk of a heart attack or stroke. Low-dose aspirin may be used:

  • After a heart attack, to prevent another one.
  • By people who have coronary artery disease.
  • By people with stable angina.
  • By people with unstable angina.
  • After bypass surgery or angioplasty.
  • By people who have had a stroke or transient ischemic attack (TIA).
  • After surgery to prevent a stroke (carotid endarterectomy).
  • By healthy men over age 45 when the benefits of aspirin to prevent a heart attack are greater than the risk of stomach bleeding from taking daily aspirin.
  • By healthy women over age 55 when the benefits of aspirin to prevent a stroke are greater than the risk of stomach bleeding from taking daily aspirin.

If you have atrial fibrillation and cannot take or choose not to take warfarin, you may take an adult-strength aspirin (325 mg) every day to help lower the risk of a stroke.

Aspirin protects you from having a clot-related stroke in the same way it protects you from having a heart attack.

Aspirin slows the blood's clotting action by reducing the clumping of platelets. Platelets are cells that clump together and help to form blood clots. Aspirin keeps platelets from clumping together, thus helping to prevent or reduce blood clots.

During a heart attack, blood clots form in an already-narrowed artery and block the flow of oxygen-rich blood to the heart muscle (or to part of the brain, in the case of stroke). When taken during a heart attack, aspirin slows clotting and decreases the size of the forming blood clot. Taken daily, aspirin's anti-clotting action helps prevent a first or second heart attack.

Aspirin should not be taken if you think you are having a stroke, because not all strokes are caused by clots. Aspirin could make some strokes worse.

Should I take aspirin?

Daily aspirin is not right for everyone. Don't start taking aspirin regularly without talking to your doctor first. Aspirin's anti-clotting action can cause unwanted side effects such as stomach bleeding and bleeding in the brain. People who have stomach ulcers, a history of gastrointestinal bleeding, blood-clotting disorders, uncontrolled high blood pressure, and liver or kidney disease may need to avoid aspirin.

Aspirin should not be taken by people who are at risk for or who have had a hemorrhagic stroke, which is a type of stroke that is not caused by a blood clot but rather by bleeding into and around the brain.

Aspirin can trigger asthma attacks in some people who have a sensitivity to it.

Also, don't take aspirin without first talking to your doctor if you're already taking prescribed blood thinners, such as Coumadin. The combined effect could cause bleeding problems.

What should I avoid when taking low-dose aspirin therapy?

Drinking 3 or more alcoholic drinks every day while taking daily aspirin increases your risk for liver damage and stomach bleeding. If your doctor recommends aspirin, limit or stop alcohol usage.

Aspirin should not be taken with many prescription and over-the-counter drugs, vitamins, herbal remedies, and supplements. So, before you start aspirin therapy, talk to your doctor about all the drugs and other remedies you take.

Because aspirin reduces your blood's ability to clot, your doctor may want you to stop taking aspirin at least 5 days before any surgery or dental procedure that may cause bleeding. Do not suddenly stop taking aspirin without talking to your doctor first. Talking to your doctor first is especially important if you have had a stent placed in a coronary artery.

Tell your doctor if you notice that you bruise easily, have bloody or black stools, or have prolonged bleeding from cuts or scrapes.

Although nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and naproxen, relieve pain and inflammation much like aspirin does, they do not affect blood clotting in the same way that aspirin does. Do not substitute NSAIDs for aspirin because they will not decrease your risk of another heart attack.

If you need both aspirin and a pain reliever every day, talk to your doctor about what pain reliever you should take. If you take uncoated aspirin and ibuprofen at the same time, the aspirin may not work as well to prevent a heart attack. You may be able to use acetaminophen instead of ibuprofen to treat your pain. But if ibuprofen is your only option, avoid taking it during the 8 hours before and the 30 minutes after your aspirin dose.4 For example, you can take ibuprofen 30 minutes after your aspirin dose. If you take ibuprofen once in a while, it does not seem to cause problems.

Experts do not know if NSAIDs other than ibuprofen interfere with uncoated aspirin. Also, experts do not know if people who take a daily coated aspirin should be concerned about ibuprofen or other NSAIDs interacting with the aspirin. Talk to your doctor if you take these medicines every day.

Exactly how much aspirin should I take?

This is where it gets confusing. Aspirin comes in a wide range of dosages and in many forms. The best dose of aspirin has not been established. Your doctor can provide the correct directions for use. Using aspirin correctly gives you the best chance of getting the greatest benefits with the fewest unwanted side effects.

Some doctors recommend taking low-dose aspirin (at least 75 mg/day), because a low dose seems to be as effective in preventing heart attacks as higher doses.

One low-dose aspirin contains 81 mg; one adult-strength aspirin contains about 325 mg. Some doctors recommend taking 100 mg every other day. Take aspirin with food if it bothers your stomach.

Also, some drug companies combine aspirin with other ingredients, such as caffeine and sodium. These formulas should not be used for daily aspirin therapy.



  1. Gaziano JM, et al. (2008). Primary and secondary prevention of coronary heart disease. In P Libby et al., eds., Braunwald's Heart Disease, 8th ed., pp. 1119–1146. Philadelphia: Saunders Elsevier.
  2. Lip GYH, et al. (2006). Stroke prevention, search date September 2005. Online version of BMJ Clinical Evidence. Also available online: http://www.clinicalevidence.com.
  3. Danchin N, Durand E (2006). Acute myocardial infarction, search date August 2004. Online version of BMJ Clinical Evidence. Also available online: http://www.clinicalevidence.com.
  4. U.S. Food and Drug Administration (2006). Concomitant use of ibuprofen and aspirin: Potential for attenuation of the anti-platelet effect of aspirin. Food and Drug Administration Science Paper. September 8, 2006. Available online: http://www.fda.gov/cder/drug/infopage/ibuprofen/science_paper.htm.

Other Works Consulted

  • U.S. Preventive Services Task Force (2009). Aspirin for the Prevention of Cardiovascular Disease. Rockville, MD: Agency for Healthcare Research and Quality. Available online: http://www.ahrq.gov/clinic/uspstf/uspsasmi.htm.


Author Robin Parks, MS
Editor Kathleen M. Ariss, MS
Associate Editor Pat Truman, MATC
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Specialist Medical Reviewer George Philippides, MD - Cardiology
Last Updated May 5, 2008

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