How Does Your Diet Affect Warfarin?

Medically Reviewed by Jennifer Robinson, MD on March 20, 2024
3 min read

Warfarin (Coumadin) is part of a group of drugs called anticoagulants. They help stop your blood from getting thicker, or “clotting.” You might hear these meds called “blood thinners.” But anticoagulants don’t actually thin your blood. They interrupt your body’s clotting process.

The food and drinks you choose and the supplements you take can affect how warfarin works. So you should always talk with your doctor before you make any big changes to how you eat and what you take.

Certain types of food, drinks, and supplements impact warfarin more than others.

Besides being an anticoagulant, warfarin is also something called a vitamin K antagonist. That means it stops your liver from turning vitamin K into substances that normally help clot your blood.

Warfarin won't work as well if you suddenly add more vitamin K to your diet. Your blood might clot when it doesn't need to. That can lead to things like a stroke or a blood clot in one of the arteries that goes from your heart to your lungs. (Your doctor may call it a pulmonary embolism.)

On the other hand, if you stop taking in vitamin K altogether, your dose of warfarin may become too strong. That could bring serious side effects like unnecessary bleeding. Also, if you start to bleed, it may be tougher to stop.

A lot of foods have high amounts of vitamin K, including:

  • Asparagus
  • Broccoli
  • Brussels sprouts
  • Cabbage
  • Collards
  • Edamame
  • Greens, like turnips and beets
  • Kale
  • Lettuce
  • Onions
  • Parsley
  • Soybeans
  • Spinach
  • Watercress

Green tea has vitamin K, as well as other compounds that can make you blood clot needlessly. Talk to your doctor about if it's OK for you to have it.

Some nutritional shakes have lots of vitamin K, too. Make sure you talk with your doctor before you make one of them part of your daily routine.

It’s a good idea to try to keep the amount of vitamin K you have each day fairly consistent. Keep track of your INR number (the measurement of how quickly your blood clots) and note how it changes after you eat certain things. You can get your INR tested at your doctor's office, or there are home tests available. Talk with your doctor about which method is best for you.

Some experts believe that cranberry and grapefruit juices can affect how warfarin works. But more evidence is needed to know for sure.

In the meantime, it’s good to be aware. If you drink these juices, you may want to limit yourself to just a glass or two each day.

If you take warfarin, don't drink lots of alcohol in a short period of time -- like at a single meal. That can change your INR and raise your chance of serious bleeding or injury.

As long as you enjoy it in moderation -- 1 to 2 servings a day -- alcohol shouldn’t be a problem. A serving is:

  • 5 ounces of wine
  • 12 ounces of beer
  • 1.5 ounces of hard liquor

A number of herbal and over-the-counter supplements can also change how your warfarin works. Some can make your blood clot when it doesn't need to, while others can help make you bleed too much.

Ones that can make clotting more likely include:

  • Ginseng
  • St. John’s wort
  • Coenzyme Q10

Supplements that may help make you bleed more include:

Most multivitamins have both vitamin K and vitamin E in them. If you're taking one now, make sure that you continue to take it every day. If you don't usually take a multivitamin, make sure your doctor thinks it's a good idea before you start taking one.