Using Blood Thinners (Anticoagulants)

Blood thinners or anticoagulants are medicines that help prevent blood clots from forming. They include warfarin, heparin, dabigatran, rivaroxaban, apixaban, and edoxaban. Your healthcare provider will help you decide which medicine is best for you.

Woman having blood drawn by phlebotomist.

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 healthcare provider gives you.

  • You may be told you need regular lab testing while taking these medicines. Warfarin requires routine testing while the other medicines do not.

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

  • Tell any healthcare 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 medicine makes bleeding harder to stop. To protect yourself:

    • Don't do any activities that may cause injury. If you fall or are injured, contact your healthcare 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.

Warfarin: Other important information

Several precautions are especially important when you are taking warfarin. Always keep these points in mind:

  • Be sure to follow your healthcare 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 to find out how much to take. Don't take a double dose.

  • Warfarin is an effective medicine, but it can be dangerous if not taken correctly. It makes your blood less likely to form clots. If you take too much, it can cause serious 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 ratio (INR) and prothrombin time (PT). These tests show how quickly your blood clots. You will also have a complete blood count (CBC) once in a while. This looks at your blood and platelet levels. Both of these need to be followed while you're on warfarin. Talk with your healthcare provider about whether you need to visit the clinic every week, or if services are available for monitoring in your home.

  • Certain medicines can affect your INR and PT levels. Tell your healthcare provider if there are any changes in your medicines. This includes any over-the-counter medicines, 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 amount of foods that are high in vitamin K. Talk with your healthcare 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 have a significant injury, contact your healthcare provider right away. It's important to alert your provider 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.


Warfarin: Watch your INR/PT blood levels

Two tests are used to find out how your blood is clotting. One is prothrombin time (PT), the other is the international normalized ratio (INR).

  • Go for your blood tests (INR/PT) as often as directed. Your diet and the other medicines you take can affect your INR/PT levels.

  • 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. 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, tell your doctor as soon as you get your lab results.

Warfarin: 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 warfarin works. They don't affect the other non-warfarin blood thinners. Here are some specific tips:

  • Try to keep your diet about the same each day. If you change your diet for any reason, such as for illness or to lose weight, tell your doctor.

  • 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 healthcare provider if you should not drink alcohol while you are taking a blood thinner.

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

  • Talk with your healthcare provider and pharmacist about specific foods or special diets that can affect anticoagulant levels. These include grapefruit juice, cranberries and cranberry juice, fish oil supplements, garlic, ginger, licorice, turmeric, and herbal teas and supplements.

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


When to call your healthcare provider

Call your provider right away if you have any of these:

  • 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

Medical conditions and anticoagulants

Before starting a blood thinner, tell your healthcare provider 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

Medicine interactions and anticoagulants

Many medicines interfere with the effect of blood thinners. Before starting these medicines, tell your healthcare provider about any prescription, over-the-counter, or herbal supplements you take. In particular, tell your provider about:

  • Antibiotics

  • Heart medicines

  • Cimetidine

  • Aspirin or other anti-inflammatory drugs such as ibuprofen, naproxen, ketoprofen, or other arthritis medicines

  • Medicines 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, medicine/food interactions, and warnings for these medicines. Check with your doctor, nurse, or pharmacist for any questions you have.