Warfarin and Diet

Medically reviewed by Alan Carter on May 20, 2016Written by University of Illinois-Chicago, Drug Information Group

Introduction

Warfarin is an anticoagulant, also known as a blood thinner. It’s used to prevent blood clots from forming in your blood vessels. It also treats blood clots if they do form by preventing them from getting larger. When the clots are smaller, they’re more likely to dissolve on their own. If blood clots are not treated, however, they can lead to stroke, heart attack, or other serious conditions.

There are certain steps that you can take to make warfarin as effective as possible. Although there is no specific “warfarin diet,” certain foods and drinks can make warfarin less effective. In this article, we’ll tell you how the foods you eat can affect how well your warfarin works. We will also give you an idea of which foods to avoid and tell you other important information about warfarin.

How can my diet affect warfarin?

Warfarin interferes with the way a certain clotting factor helps your blood to clot. A clotting factor is a substance that helps the blood clump together to form a clot. There are 13 types of clotting factors in every person’s blood. The type of clotting factor that warfarin interferes with is called the vitamin K-dependent clotting factor. Warfarin works by decreasing the amount of vitamin K in your body. Without enough vitamin K to use, the vitamin K-dependent clotting factor can’t help your blood to clot like it usually does.

Your body makes vitamin K, but it also gets it from certain foods you eat. One way you can help warfarin work its best is by avoiding big changes in the amount of vitamin K you get through food. Warfarin works because you usually have consistent levels of vitamin K in your body. If you change the amount of vitamin K you get through food, it can change the levels of vitamin K in your body. This can affect how warfarin works for you.

Foods to limit while taking warfarin

If you suddenly start eating foods that have more vitamin K while you take warfarin, you may make warfarin less effective for you. If you suddenly start eating foods that have less vitamin K while you take warfarin, you may increase your chances of side effects from warfarin.

Foods that are rich in vitamin K include leafy vegetables. These may make warfarin less effective. Examples include:

  • Kale
  • Spinach
  • Brussels sprouts
  • Parsley
  • Collard greens
  • Mustard greens
  • Endive
  • Red cabbage
  • Green lettuce
  • Chard

You should also avoid drinking:

  • Green tea
  • Grapefruit juice
  • Cranberry juice
  • Alcohol

Green tea contains vitamin K and could lower the effectiveness of warfarin. Drinking grapefruit juice, cranberry juice, and alcohol during treatment with warfarin can increase your risk of bleeding.

While you take warfarin, your doctor will check your blood regularly to see how well the drug is working for you.

What else can affect warfarin and how?

Substances other than food can also affect how warfarin works. This effect is called an interaction. Sometimes, these interactions can increase your risk of side effects from warfarin as well.

Interactions

In addition to food, many other substances can interact with warfarin. These include medications, supplements, and herbal products. Tell your doctor all of the medications you’re taking before you start taking warfarin. Some medications that can interact with warfarin include:

  • antibiotics such as ciprofloxacin or fluconazole
  • certain birth control pills
  • certain drugs for seizures
  • anti-inflammatory drugs such as ibuprofen
  • antidepressants such as fluoxetine
  • other blood thinners such as aspirin, clopidogrel, or heparin
  • certain antacids

Supplements and herbal products that can interact with warfarin include:

  • gingko biloba
  • garlic
  • co-enzyme Q10
  • St. John’s wort

Side effects

Interactions with food, medications, and other substances can also increase your risk of side effects from warfarin. The most common side effects of warfarin include:

  • allergic reactions
  • gastrointestinal disorders
  • rash
  • hair loss
  • itchy skin
  • chills
  • inflammation of your blood vessels
  • liver or gall bladder disorders

Some serious side effects of warfarin can include:

  • excessive bleeding from wounds
  • death of skin tissue, caused by small blood clots that block the flow of oxygen to your skin
    • Check your toes often, especially if you feel discomfort. Toe pain can be a symptom of skin death.

Learn more: Warfarin dosage, side effects, interactions, warnings, and more >>

Pharmacist advice

You should always try to make a habit of eating healthy foods. However, it’s especially important to pay attention to what you eat and how much you eat while you take warfarin. The following rules of thumb can help you ensure that warfarin works its best for you:

  • Don’t make any big changes to your diet, especially in the amount vitamin K-rich foods.
  • Avoid green tea, cranberry juice, grapefruit juices, and alcohol.
  • Tell your doctor about other medications, supplements, and herbal products you take.

Following these tips will help you avoid interactions and keep your nutrient levels consistent. This will help make warfarin as effective as possible. It will also help reduce your risk of side effects.

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