How Coumadin Helps With Stroke Prevention

Coumadin (warfarin) is a blood thinning medication that works by inhibiting the function of vitamin K—an essential factor in the body's ability to form blood clots.

A doctor discusses stroke prevention with his patient
John Fedele / Getty Images

Coumadin and Strokes

Coumadin is a powerful medication used for stroke prevention. Coumadin has potent blood-thinning properties (i.e., it prevents the abnormal formation of blood clots in the body). An example of a disease in which abnormal blood clot formation leads to stroke is atrial fibrillation, a disease in which an erratic beating of the heart leads to the formation of unwanted blood clots inside the heart chambers. Other instances in which Coumadin is used for stroke prevention include:

  • When someone had a defective heart valve replaced surgically with a mechanical prosthetic valve.
  • When someone is found to have a blood clot inside the heart after they suffered a heart attack.
  • When someone is found to have a blood clot in the deep veins in the legs (also known as deep venous thrombosis or DVT. DVTs can cause strokes in people who have a small hole between the right and left sides of the heart. This small hole is known as patent foramen ovale or PFO.
  • When someone has an abnormal tendency to form blood clots as a result of an autoimmune disorder, such as lupus.
  • When someone has a genetic predisposition to form blood clots due to a deficiency in one or more of the body’s mechanisms that normally prevent abnormal blood clot formation.

International Normalized Ratio (INR)

Blood clotting is measured using the International Normalized Ratio (INR), which attributes a value of 1.0 to people with a normal ability to form blood clots. When people take Coumadin, their INR increases, an indication that they are less likely to form blood clots.

The desirable INR for stroke prevention is between 2-3, though this range may vary depending on the condition being treated. The INR is measured with a blood test. If the INR goes too high (more than 3) this can cause unwanted bleeding. This is the reason why people who take Coumadin must have their blood drawn every few weeks or months.

Blood Pressure Control

People who suffer from high blood pressure and who also take Coumadin for stroke prevention must always keep in mind that high blood pressure increases the risk of hemorrhagic strokes or strokes caused by bleeding in the brain. As Coumadin decreases the body’s mechanisms which normally stop bleeding, people who take Coumadin must always keep their blood pressure in check.


  • Take only medicines prescribed by your healthcare provider (Coumadin interacts with multiple medications).
  • Take your Coumadin at the same time every day (usually before bedtime).
  • Eat the same amount of vitamin K-containing food every day (e.g., fish, broccoli, spinach, cabbage, kale, cauliflower).
  • Avoid excessive alcohol.
  • Avoid activities which might cause you to fall.
  • Never stop Coumadin without your practitioner's knowledge.
  • Never take double doses of Coumadin, unless specifically asked by your healthcare provider to do so.
  • Call your practitioner if your stool changes in color.
9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. MedlinePlus. Blood Thinners.

  3. U.S. Pharmacist. Antithrombotic Therapy in Patients With Valvular Heart Disease.

  4. UpToDate. Patient Education: Deep vein thrombosis (DVT) (Beyond the Basics).

  5. John Hopkins Lupus Center. Anticoagulants.

  6. Low INR to Minimize Bleeding With Mechanical Valves Trial (LIMIT).

  7. Heran BS, Allan GM, Green L, et al. Effect of medication timing on anticoagulation stability in users of warfarin (The inrange rct): study protocol for a randomized controlled trial. Trials. 2016;17(1):391. doi. 10.1186%2Fs13063-016-1516-9

  8. American Heart Association. How High Blood Pressure Can Lead to Stroke.

  9. American Heart Association. A Patient's Guide to Taking Warfarin.

By Jose Vega MD, PhD
Jose Vega MD, PhD, is a board-certified neurologist and published researcher specializing in stroke.