Low-Dose ASA Therapy

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Low-Dose ASA Therapy

Topic Overview

Why take low-dose ASA?

Good old ASA, the common pain reliever that has been in our medicine cabinets for almost a century, also has a talent for prevention.

For people who have had a heart attack: ASA can help prevent a second heart attack.

For people who have had a stroke: ASA can help prevent a second stroke or a transient ischemic attack (TIA), which is often a warning sign of an impending stroke.

For people who have never had a heart attack or stroke: ASA may reduce your chance of having a heart attack or a stroke if you have certain risk factors, such as diabetes, high blood pressure, high cholesterol, or smoking. If you have a higher risk for a heart attack or stroke, ASA will have even more benefit for you.

Who should take low-dose ASA?

If you have had a heart attack or stroke, your doctor has probably already prescribed low-dose ASA for you.

If you have never had a heart attack or stroke, talk to your doctor before you start taking ASA every day.

Doctors use different guidelines to decide who should take daily ASA. But no matter which guideline your doctor follows, he or she will look at your health and at your risk for a heart attack or stroke. Then you and your doctor will balance the benefits and the risks of taking a daily ASA to see if a daily ASA is right for you. For help on the decision to take low-dose ASA, see:

Click here to view a Decision Point. ASA: Should I Take Daily ASA to Prevent a Heart Attack or Stroke?

If you have a higher risk for a heart attack or stroke, ASA will have even more benefit for you. If the benefit of ASA is more than the risk of side effects, you may want to take daily ASA.

Daily ASA isn't advised for people who have a low risk of heart attack or stroke.

Your doctor can help you know your risk of having a heart attack or stroke and the risk of bleeding from ASA. If you know your blood pressure and cholesterol numbers, you can use this Interactive Tool: Are You at Risk for a Heart Attack? to find out your risk.

Low-dose ASA 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 ASA to prevent a heart attack are greater than the risk of stomach bleeding from taking daily ASA.
  • By healthy women over age 55 when the benefits of ASA to prevent a stroke are greater than the risk of stomach bleeding from taking daily ASA.

If you have atrial fibrillation and have a low risk of stroke, you might take ASA to help lower your risk of stroke. ASA may be a good choice if you are young and have no other heart or health problems or if you can't take an anticoagulant (also called a blood thinner) safely.

Who should not take low-dose ASA?

Some people shouldn't take ASA. These include people who:

  • Have a stomach ulcer.
  • Have recently had a stroke caused by bleeding in the brain.
  • Are allergic to ASA.
  • Have high blood pressure that isn't under control.
  • Have asthma that is made worse by ASA.

Daily ASA isn't advised for people who have a low risk of heart attack or stroke.

If you think you are having a stroke, do not take ASA because not all strokes are caused by clots. ASA could make some strokes worse.

Gout can become worse or hard to treat for some people who take low-dose ASA.

If you can't take ASA, your doctor may have you take clopidogrel (Plavix) to help prevent a heart attack or a stroke.

If you take an anticoagulant, such as warfarin (Coumadin), talk with your doctor before taking ASA, because taking both medicines can cause bleeding problems.

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

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

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

Because ASA reduces your blood's ability to clot, your doctor may want you to stop taking ASA at least 5 days before any surgery or dental procedure that may cause bleeding. Do not suddenly stop taking ASA 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 non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and naproxen, relieve pain and inflammation much like ASA does, they do not affect blood clotting in the same way that ASA does. Do not substitute NSAIDs for ASA, because they will not decrease your risk of another heart attack.

If you need both ASA and a pain reliever every day, talk to your doctor about what pain reliever you should take. If you take uncoated ASA and ibuprofen at the same time, the ASA 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 ASA dose. For example, you can take ibuprofen 30 minutes after your ASA 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 ASA. Also, experts do not know if people who take a daily coated ASA should be concerned about ibuprofen or other NSAIDs interacting with the ASA. Talk to your doctor if you take these medicines every day.

How do you take low-dose ASA?

Your doctor will recommend a dose of ASA and how often to take it. Most people take ASA every day to help prevent a heart attack or a stroke, but others might take ASA every other day.

Low-dose ASA (81 mg) is the most common dose used to prevent a heart attack or a stroke. But the dose for daily ASA can range from 81 mg to 325 mg. One low-dose ASA contains 81 mg. One adult-strength ASA contains about 325 mg.

Low-dose ASA seems to be as effective in preventing heart attacks and strokes as higher doses.

Take ASA with food if it bothers your stomach.

For low-dose ASA therapy, do not take medicines that combine ASA with other ingredients such as caffeine and sodium.

How does ASA work to prevent a heart attack or stroke?

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

ASA slows the blood's clotting action by reducing the clumping of platelets. Platelets are cells that clump together and help to form blood clots. ASA 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, ASA slows clotting and decreases the size of the forming blood clot. Taken daily, ASA's anti-clotting action helps prevent a first or second heart attack.

Other Places To Get Help


Canadian Cardiovascular Society
222 Queen Street
Suite 1403
Ottawa, ON  K1P 5V9
Phone: 1-877-569-3407 toll-free
(613) 569-3407
Fax: (613) 569-6574
Web Address: www.ccs.ca

The Canadian Cardiovascular Society works to advance the cardiovascular health and care of Canadians through leadership, research, and advocacy.

Heart and Stroke Foundation of Canada
222 Queen Street
Suite 1402
Ottawa, ON  K1P 5V9
Phone: (613) 569-4361
Fax: (613) 569-3278
Web Address: www.heartandstroke.ca

The Heart and Stroke Foundation of Canada works to improve the health of Canadians by preventing and reducing disability and death from heart disease and stroke through research, health promotion, and advocacy.

U.S. National Heart, Lung, and Blood Institute (NHLBI)
P.O. Box 30105
Bethesda, MD  20824-0105
Phone: (301) 592-8573
Fax: (240) 629-3246
TDD: (240) 629-3255
Email: nhlbiinfo@nhlbi.nih.gov
Web Address: www.nhlbi.nih.gov

The U.S. National Heart, Lung, and Blood Institute (NHLBI) information center offers information and publications about preventing and treating:

  • Diseases affecting the heart and circulation, such as heart attacks, high cholesterol, high blood pressure, peripheral artery disease, and heart problems present at birth (congenital heart diseases).
  • Diseases that affect the lungs, such as asthma, chronic obstructive pulmonary disease (COPD), emphysema, sleep apnea, and pneumonia.
  • Diseases that affect the blood, such as anemia, hemochromatosis, hemophilia, thalassemia, and von Willebrand disease.


Other Works Consulted

  • American Heart Association and American College of Cardiology (2006). AHA/ACC guidelines for secondary prevention for patients with coronary and other atherosclerotic vascular disease: 2006 update. Circulation, 113(19): 2363–2372. [Erratum in Circulation, 113(22): 847.]
  • Antiplatelet and anticoagulant drugs (2008). Treatment Guidelines From The Medical Letter, 6(69): 29–36.
  • Antiplatelet therapy for patients with stents. (2008). Medical Letter on Drugs and Therapeutics, 50(1292): 61–63.
  • Steinhubl SR, et al. (2009). Aspirin to prevent cardiovascular disease: The association of aspirin dose and clopidogrel with thrombosis and bleeding. Annals of Internal Medicine, 150(6): 379–386.
  • 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/downloads/Drugs/DrugSafety/PostmarketDrugSafetyInformationforPatientsandProviders/UCM161282.pdf.
  • 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.


By Healthwise Staff
Primary Medical Reviewer Kathleen Romito, MD - Family Medicine
Primary Medical Reviewer Brian D. O'Brien, MD - Internal Medicine
Specialist Medical Reviewer George Philippides, MD - Cardiology
Specialist Medical Reviewer Stephen Fort, MD, MRCP, FRCPC - Interventional Cardiology
Last Revised January 18, 2011

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