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Stroke Prevention: Using Blood Thinners (Anticoagulants)

During a stroke, a blood clot stops blood from flowing to part of the brain. If you have had a stroke or are at risk for one, or have certain other risk factors, you may be prescribed a medication to prevent blood clots. These are anticoagulants, commonly called blood thinners. They can make it less likely that you will have a blood clot that leads to a stroke.

Types of anticoagulants

Blood thinners help prevent blood clots from forming. They include warfarin, heparin, dabigatran, rivaroxaban, and apixaban. Your doctor will help you decide which is best for you.

Taking an anticoagulant safely

When you are taking a blood thinner, you will need to take certain steps to stay safe. Too much blood thinner puts you at risk for bleeding. Too little puts you at risk for stroke. Follow these guidelines. Also follow any others that your health care provider gives you.

  • You may be told you need regular testing to check the levels of this medication in your blood. Keep all of your appointments for these tests.

  • Tell your doctor about all medications you take. This includes over the counter medications, supplements, or herbal remedies. Do not take any medications (including ones you buy over the counter) that your doctor doesn’t know about. Some medications can interact with blood thinners and cause serious problems.

  • Tell any health care provider that you see for care (such as doctors, dentists, chiropractors, home health nurses) that you take a blood thinner.

  • Carry a medical ID card or wear a medical-alert bracelet that says you take an anticoagulant.

  • Before taking aspirin, check with your doctor. Aspirin can significantly increase your risk of bleeding.

  • This medication makes bleeding harder to stop. To protect yourself:

    • Avoid activities that may cause injury. If you fall or are injured, contact your health care provider right away. Blood thinners prevent clotting, so you could be bleeding inside without realizing it.

    • Use a soft-bristle toothbrush and waxed dental floss. Shave with an electric razor rather than a blade.

    • Don’t go barefoot. Don’t trim corns or calluses yourself.

If you are taking warfarin, several precautions are especially important. Always keep in mind the following:

  • Be sure to follow your health care provider's instructions for taking warfarin.

  • Take this medicine at the same time each day. Take it with a full glass of water, with or without food. If you miss a dose, contact your doctor immediately to find out how much to take. Never take a double dose.

  • Warfarin is an effective drug, but it can be dangerous if not take properly. It makes your blood less likely to form clots. If you take too much, it can cause too much internal or external bleeding.

  • You will need to have regular monitoring while you are taking warfarin. This includes blood tests to check your International Normalized Ration (INR) and prothrombin time (PT) -- indicators of how quickly your blood clots. You will also have a complete blood count (CBC), which tests your blood and platelet level, both of which need to be followed while you're on blood thinners. Talk with your health care provider about whether you need to visit the clinic every week, or if services are available for monitoring in your home.

  • Certain medications can affect your INR and PT levels. Never take, or stop taking, any medication without talking to your health care provider first. This includes any over-the-counter medications, supplements (like vitamin K), or herbal remedies.

  • Your diet can also affect your INR and PT levels. Because of this, it's important to eat a consistent diet. It is especially important to eat a consistent about of foods that are high in vitamin K. Be sure to talk with your health care provider before making any big changes in your diet.

  • Remember that warfarin increases your risk of bleeding. Be careful not to injure yourself. If you do injure yourself, contact your health care provider right away. It's important to alert your doctor if you've fallen or hurt yourself, even if you don't break your skin. You could be bleeding inside your body without realizing it.

Monitoring your INR/PT blood levels after discharge

Two tests are used to find out how your blood is clotting. One is protime (PT) the other is the International Normalized Ratio (INR).

  • Go for your blood tests (INR/PT) as often as directed. Note that diet and medication can affect your INR/PT levels.

  • Your INR was between ___ and ___.

  • As your doctor what your goal INR is. My goal INR is between ___ and ___.

  • My next INR/PT blood draw is due on _____________(date) at ___________(time) by ___________ (name of doctor or clinic).

  • The name of the doctor who is monitoring my anticoagulation therapy is _____________________ and the phone number is _________________.

  • Follow up with your doctor or as advised by his or her staff. It usually takes a few hours for your doctor to get the results of your clotting tests. Please call to get your lab results to find out if your doctor needs to make further changes to your warfarin dose.

  • If your blood is drawn for these tests at a location other than your doctor's office, please remember to tell your doctor as soon as you get your lab results.

Watch what you eat

Vitamin K helps your blood clot. So you have to watch how much you eat of foods that contain vitamin K. These foods can affect the way your anticoagulant works. Here are some specific tips:

  • Try to keep your diet about the same each day.

  • Each day, eat the same amount of foods that are high in vitamin K. These include asparagus, avocado, broccoli, cabbage, kale, spinach, and some other leafy green vegetables. Oils, such as soybean, canola, and olive oils, are also high in vitamin K.

  • Limit fats to 2 to 4 tablespoons a day.

  • Ask your health care provider if you should avoid alcohol while you are taking a blood thinner.

  • Avoid teas that contain sweet clover, sweet woodruff, or tonka beans. These can affect how your medication works.

  • Consult with your doctor and pharmacist about specific foods or special diets that can affect anticoagulant levels, such as grapefruit juice.

  • Keep your diet pretty much the same each day. If you change your diet for any reason, such as due to illness or to lose weight, be sure to tell your doctor.

  • Other food products can affect the way warfarin works in your body including cranberries and cranberry juice, fish oil supplements, garlic, ginger, licorice, turmeric, herbal teas and supplements, and alcohol.

Talk with your health care provider if you have concerns about these or other food products and their effects on warfarin.

When to call your doctor

Call your doctor right away if you have any of the following:

  • Bleeding that doesn’t stop in 10 minutes

  • A heavier-than-normal menstrual period or bleeding between periods

  • Coughing or throwing up blood

  • Bloody diarrhea or bleeding hemorrhoids 

  • Dark-colored urine or black stools

  • Red or black-and-blue marks on the skin that get larger

  • Dizziness or fatigue

  • Chest pain or trouble breathing

Allergic reactions:

  • Rash

  • Itching

  • Swelling

  • Trouble swallowing or breathing

IMPORTANT:  Medical conditions

Before starting an anticoagulant, be sure your doctor knows if you have any of these conditions:

  • Stomach ulcer now or in the past

  • Vomited blood or had bloody stools (black or red color)

  • Aneurysm, pericarditis, or pericardial effusion

  • Blood disorder

  • Recent surgery, stroke, mini-stroke, or spinal puncture

  • Kidney or liver disease, uncontrolled high blood pressure, diabetes, vasculitis, heart failure, lupus, or other collagen-vascular disease, or high cholesterol

  • Pregnancy or breastfeeding

  • Younger than 18 years old

  • Recent or planned dental procedure

IMPORTANT: Drug interactions

Many medicines interfere with the effect of warfarin. Before starting this medicine, be sure your doctor knows about any prescription, over-the-counter, or herbal supplements you take. Especially:

  • Antibiotics

  • Heart medicines

  • Cimetidine (Tagamet)

  • Aspirin or other anti-inflammatory drugs such as ibuprofen (Advil, Motrin, or Nuprin), naproxen (Aleve, naprosyn, Anaprox), ketoprofen (Orudis, Oruvail), or other arthritis medicines

  • Drugs for depression, cancer HIV (protease inhibitors), diabetes, seizures, gout, high cholesterol, or thyroid replacement

  • Vitamins containing vitamin K or herbal products such as ginkgo, Co-Q10, garlic, or St. John's wort

Note: This information topic may not include all directions, precautions, medical conditions, drug/food interactions, and warnings for this drug. Check with your doctor, nurse, or pharmacist for any questions you have.

Online Medical Reviewer: Foster, Sarah, RN, MPH
Online Medical Reviewer: MMI board-certified, academically affiliated clinician
Last Review Date: 3/31/2014
© 2000-2014 The StayWell Company, LLC. 780 Township Line Road, Yardley, PA 19067. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.