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Using Blood Thinners (Anticoagulants)

Blood thinners are medicines that help prevent blood clots from forming. They are also called anticoagulants. The medicines include:

  • Warfarin

  • Heparin

  • Dabigatran

  • Rivaroxaban

  • Apixaban

  • Edoxaban

  • Betrixaban

Your healthcare provider will talk with you about which medicine is best for you.

Woman having blood drawn by phlebotomist.

Before you start taking a blood thinner

Before starting your medicine, tell your healthcare provider if you have any of these:

  • Stomach ulcer, now or in the past

  • Vomiting of blood

  • Blood in your stool (black or red color)

  • Aneurysm

  • Pericarditis

  • Pericardial effusion

  • Blood disorder

  • Recent surgery

  • Stroke or ministroke (called a TIA)

  • Spinal puncture

  • Kidney or liver disease

  • Uncontrolled high blood pressure

  • Diabetes

  • Vasculitis

Also tell your healthcare provider if any of these apply to you:

  • You're younger than 18 years old.

  • You had a recent dental procedure or have one planned.

  • You are pregnant or breastfeeding.

This list may not include all conditions that can affect how your medicine works. Talk with your healthcare provider and pharmacist.

Medicines that interact with blood thinners

Many medicines change how blood thinners work. Before taking a blood thinner, tell your healthcare provider about all medicines and supplements you take. This includes prescription and over-the-counter medicines, vitamins, or herbs. Tell your healthcare provider if you take:

  • Antibiotic medicine

  • Heart medicine

  • Cimetidine

  • Anti-inflammatory medicine, such as aspirin, ibuprofen, naproxen, ketoprofen, or arthritis medicine

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

  • Multivitamins that have vitamin K

  • Herbs, such as ginkgo, Co-Q10, garlic, or St. John's wort

This list may not include all medicines and supplements that can affect how your medicine works. Talk with your healthcare provider and pharmacist.

Taking a blood thinner safely

When you are taking a blood thinner, you will need to take care 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.

  • Have regular blood tests as advised. Warfarin requires regular testing at least once a month. The other medicines such as antiplatelet drugs do not require regular testing.

  • Tell your healthcare provider about all medicines you take. This includes over-the-counter medicines, vitamins, or herbal remedies. Don't take any medicines that your healthcare provider doesn’t know about. This includes ones you buy over the counter. Some medicines can affect how blood thinners work. This can cause serious problems.

  • Tell all of your healthcare providers that you take a blood thinner. This includes your dentist, chiropractor, home health nurse, and other healthcare providers.

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

  • Before taking aspirin, check with your healthcare provider. Aspirin can greatly increase your risk of bleeding.

Blood thinners make bleeding harder to stop. Even a small injury could cause a lot of bleeding. An injury can cause bleeding inside your body that you don’t know about. To protect yourself:

  • Don't do any activities that may cause injury.

  • 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.

Important safety information

Be extra careful when you are taking a blood thinner. Always:

  • Take it exactly as prescribed. Follow your healthcare provider's instructions. Blood thinners can be dangerous if not taken correctly. They make your blood less likely to form clots. If you take too much, it can cause serious internal or external bleeding.

  • Take it at the same time each day. Take it with a full glass of water, with or without food. If you miss a dose, call your healthcare provider to find out how much to take. Don't take a double dose.

  • Have regular blood tests. You may need to have regular tests while you are taking blood thinners. These may include blood tests to check your international normalized ratio (INR) and prothrombin time (PT). These tests show how fast 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 watched while you're on warfarin. Ask your healthcare provider if you need to visit the clinic every week. You can also find out if your blood can be tested at home. Ask your provider how often you will need your blood tested for the blood thinner you are taking.

  • Tell your healthcare provider about changes in your medicines.  Some medicines can affect your INR and PT levels. This includes any over-the-counter medicines, supplements like vitamin K, or herbal remedies.

  • Keep your diet the same. What you eat can also affect your INR and PT levels. So eat a consistent diet. It's most important to eat the same amount of foods that are lower in vitamin K, because it can affect the way the blood thinner works. Talk with your healthcare provider before making any changes in your diet.

  • Be careful not to injure yourself. Remember that warfarin increases your risk of bleeding. If you have a severe injury and are concerned about internal or external bleeding, go to the emergency room.

Blood thinners: Getting regular blood tests

You will have 2 tests to find out how your blood is clotting. One is called prothrombin time (PT). The other is called the international normalized ratio (INR).

  • Get your blood tests as often as directed.

  • Follow up with your healthcare provider as advised. It may take a few hours for them to get your results. Call to find out your lab results. Ask your healthcare provider if you need to make changes to your dose or diet.

  • If your blood tests are not done at your healthcare provider’s office, tell them as soon as you get your test results.

My next INR/PT blood test is on _____________ (date) at ___________ (time) by ___________ (name of healthcare provider or clinic).

The name of the healthcare provider who is in charge of my anticoagulation therapy is _____________________. The phone number is _________________.

Watching what you eat

Vitamin K is a nutrient found in some foods. Vitamin K helps your blood clot. Because of this, you may need to watch how much you eat of foods that have vitamin K. These foods can affect the way your blood thinner works.

  • 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 healthcare provider.

  • Each day, eat the same amount of foods that are lower in vitamin K. These include asparagus, avocado, broccoli, cabbage, kale, spinach, and some other leafy green vegetables.

  • Limit oils that are high in vitamin K to 2 to 4 tablespoons a day. This includes oils such as soybean, canola, and olive

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

  • Don't drink teas that contain sweet clover, sweet woodruff, or tonka beans.

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

This list may not include all foods and ingredients that can affect how your medicine works. Talk with your healthcare provider and pharmacist.

When to call your healthcare provider

Call your healthcare provider or seek medical care right away if you have any of these:

  • Bleeding that doesn’t stop in 10 minutes

  • A heavy menstrual period or bleeding between periods

  • Coughing up or vomiting blood

  • Bloody diarrhea

  • Bleeding hemorrhoids 

  • Dark-colored urine

  • Black stools

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

  • Dizziness, lightheadedness, fainting (Call 911)

  • Chest pain (Call 911)

  • Trouble breathing (Call 911)

  • Rash

  • Itching

  • Swelling

  • Trouble swallowing

Online Medical Reviewer: Deepak Sudheendra MD
Online Medical Reviewer: Marianne Fraser MSN RN
Online Medical Reviewer: Rita Sather RN
Date Last Reviewed: 6/1/2024
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