Warfarin is an anticoagulant, or 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 clots are smaller, they’re more likely to dissolve on their own. If blood clots are not treated, they can lead to stroke, heart attack, or other serious conditions.

There are steps that you can take to help 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 foods you eat can affect how well your warfarin works
  • give you an idea of which foods to avoid
  • tell you other important information about 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’re getting through food, it can change the levels of vitamin K in your body. This can affect how warfarin works for you.

If you suddenly start eating foods that have more vitamin K while you take warfarin, you may make warfarin less effective. 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.

There are a variety of foods that are low in vitamin K that can help you create and enjoy a well-balanced diet.

Some vegetables and fruits low in vitamin K include:

  • Sweet corn
  • Onions
  • Squash
  • Eggplant
  • Tomatoes
  • Mushrooms
  • Sweet Potatoes
  • Cucumbers (raw)
  • Artichoke
  • Strawberries
  • Apples
  • Peaches
  • Watermelon
  • Pineapple
  • Bananas

For a comprehensive list of foods containing vitamin K, visit the U.S. Department of Agriculture’s composition database.

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.

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

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:

Supplements and herbal products that can interact with warfarin include:

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:

Some serious side effects of warfarin can include:

  • Excessive bleeding from wounds.
  • Death of skin tissue, which is 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.

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.