Foods to Avoid on Blood Thinners

Blood thinners, such as warfarin, apixaban, or rivaroxaban, are commonly prescribed to prevent blood clots, reduce stroke risk, or treat certain heart conditions. But while these medications can be lifesaving, their effectiveness can be impacted by the foods you eat. Some foods interfere with how these drugs work in your body, either making them too strong or not strong enough.

This article offers a comprehensive list of foods to avoid on blood thinners, and how to make safe, informed choices without giving up a healthy, varied diet.

Why Food Matters When Taking Blood Thinners

Blood thinners affect your body’s natural clotting process. Some, like warfarin, work by blocking vitamin K, a nutrient your liver uses to produce clotting proteins. To monitor how well warfarin is working, doctors track your INR (international normalized ratio), a lab test that measures how long it takes your blood to clot. For most people on warfarin, the target INR is usually between 2.0 and 3.0.

• • If it’s too low, you may be at risk for a blood clot.
  • If it’s too high, your bleeding risk goes up.

Since warfarin has a narrow safety range, even small changes, like eating more or less vitamin K, can cause INR levels to swing dangerously out of range.

Other blood thinners, like Eliquis (apixaban) or Xarelto (rivaroxaban), don’t require regular INR monitoring. But they can still be affected by certain foods, herbs, or supplements that alter how your body processes medications or how your blood clots.

That’s why diet consistency matters. If your eating habits change a lot, especially your vitamin K intake or foods that affect liver enzymes, it can throw off your treatment balance and increase your risk of complications.

20 Foods to Avoid on Blood Thinners

Here’s a list of foods to avoid while on blood thinners:

1. High-Vitamin K Vegetables

Warfarin thins your blood by slowing the action of vitamin K, which your body uses to make clotting factors. Eating large or inconsistent amounts of vitamin K can interfere with warfarin’s ability to prevent clots.

Common high-vitamin K vegetables to be mindful of:

• • Kale
  • Spinach
  • Collard greens
  • Swiss chard
  • Turnip greens
  • Broccoli
  • Brussels sprouts

However, note that warfarin’s strength depends on your vitamin K levels. If you suddenly increase your vitamin K intake, it may lower the drug’s effectiveness, putting you at risk for blood clots or stroke. At the same time, sudden drops in intake can make warfarin too strong, increasing your risk for bleeding.

Current guidelines recommend keeping intake steady, not avoiding it.

2. Green Tea, Black Tea, and Other Traditional Teas

Camellia sinensis is the plant used to make green tea, black tea, and other traditional teas. The dried tea leaves are very high in vitamin K (up to 1428 µg per 100g). But when you brew the tea, the amount of vitamin K that ends up in the drink is very low, about 0.03 µg per 100g of tea.

However, there are still real-world cases where it affected warfarin’s effectiveness. In one case, a 44-year-old man on warfarin drank half to one gallon of green tea daily. His INR dropped from 3.79 to 1.37 (a big decrease, meaning his blood became more likely to clot). When he stopped drinking green tea, his INR went back up.

Another case involves a 67-year-old woman on warfarin who stopped drinking black tea (amount unknown). Her INR jumped from 1.7 to 5.0 (much higher bleeding risk). Her warfarin dose had to be lowered.

In addition to vitamin K, other tea compounds, like catechins and caffeine, may also thin the blood by stopping platelets from clumping. If you’re on warfarin, you might want to add these drinks to your list of foods to avoid on blood thinners.

3. Pineapple and Papaya

Pineapple and papaya are among the fruits to avoid when taking warfarin due to their potential to increase bleeding risk. This happens because they contain natural enzymes:

• • Pineapple contains bromelain
  • Papaya contains papain

Bromelain can interfere with liver enzymes like CYP2C9, which affects how warfarin is broken down. It can also thin the blood on its own by stopping platelets from sticking together. Papain may have similar effects, especially when taken from unripe papaya, which contains higher amounts. It’s believed to also mildly block CYP2C9 and thin the blood.

These effects can make warfarin work too strongly, increasing the risk of dangerous bleeding.

In a real-world case, a 50-year-old woman who had been on warfarin for years with stable INR levels suddenly came to the hospital with:

• • Blood in her urine
  • Bruising on her skin
  • Internal bleeding in her abdomen
  • Swelling in one leg

Her INR was extremely high at 14.7, which means her blood was way too thin. But she hadn’t changed any meds or diet, except starting a smoothie with pineapple and papaya every other day. Since there was no other clear reason for her blood-thinning problem, it’s very likely that the fruits in her smoothie contributed to it.

4. Cranberry and Cranberry Juice

Even though the exact reason isn’t fully clear, there have been serious cases where cranberry juice increased the effects of warfarin, leading to dangerous bleeding.

Lab and animal studies suggested that cranberry might affect liver enzymes (CYP2C9 and CYP34A), which are involved in breaking down warfarin. However, human studies have not shown strong proof that cranberry changes how warfarin is processed.

Still, case reports showed problems in real life. One person died after drinking 2 cups (~300-400?mL) of cranberry juice daily for 6 weeks while on warfarin. Another case in the US involved severe bleeding and a very high INR shortly after starting cranberry juice (about 710 mL/day).

Cranberry and warfarin can be a risky combination, even though not everyone is affected, the possible bleeding risk is serious, making it among the foods to avoid on blood thinners.

5. Alcoholic Beverages

Drinking alcohol can increase your risk of internal bleeding, especially in your stomach and intestines. In fact, a 2015 study found that nearly 20% of people hospitalized for gastrointestinal (GI) bleeding were heavy alcohol users.

This risk isn’t limited to warfarin. It also applies to newer blood thinners like Eliquis (apixaban) and Xarelto (rivaroxaban).

Alcohol has a mild blood-thinning effect. Research shows that shortly after drinking, your platelets become less likely to stick together. This makes it harder for your blood to clot. It’s a weaker effect than medications like Eliquis, but it still adds to the overall bleeding risk.

One case-control study looked at 570 people taking warfarin. It found that those who drank five or more alcoholic drinks in one sitting were more than twice as likely to have serious bleeding compared to those who didn’t drink.

The 2020-2025 Dietary Guidelines for Americans recommend that women have no more than one drink per day and men no more than two. But if you’re taking a blood thinner, it’s best to avoid alcohol altogether.

6. Grapefruit and Grapefruit Juice

Similar to cranberry, even small amounts of grapefruit juice can block an enzyme called CYP3A4, which helps break down many drugs, including blood thinners.

In one case, a couple who had been stable on warfarin both took grapefruit seed extract for three days. The woman developed a small bruise, and the man’s INR jumped to 5.1, meaning his blood was too thin.

In another report, a 65-year-old man with atrial flutter was taking warfarin and had recently increased his dose slightly after a low INR reading. Two weeks later, his INR rose sharply to 4.77, even though he followed the new dosing. The only change he reported was that he had started eating grapefruit.

He wasn’t bleeding, but his dose was lowered, and he stopped eating grapefruit. A week later, his INR dropped to 2.1, and he returned to his usual dose. His INR has stayed stable since.

7. Fermented Soy Products

Soya (or soy) is commonly used in Japanese and Chinese cooking and is known for possible health benefits like lowering cholesterol and helping with menopause or bone health. However, soy products can affect how warfarin and similar blood thinners work.

Lab studies found that soy can block liver enzymes that help break down warfarin. But results from lab tests don’t always apply directly to people. Fermented soy products like natto contain a lot of vitamin K, which can weaken warfarin’s effects and make your blood more likely to clot.

In animal studies, natto reduced warfarin’s effect. In real-life cases, people taking warfarin or similar drugs saw their INR drop (blood became thicker) when they ate natto daily or drank soy milk regularly. For example, a 70-year-old man’s INR dropped from 2.5 to 1.6 after drinking soy milk every day for four weeks while on warfarin.

Other fermented soy products, like miso or tempeh, may also contain vitamin K in smaller amounts.

8. Garlic and Garlic Supplements

Fresh garlic in food is generally safe in moderate amounts, but garlic supplements or large quantities can thin the blood and increase bleeding risk.

One patient on warfarin had their INR double and developed blood in the urine after taking garlic daily for 8 weeks. Another patient’s INR also more than doubled after taking six garlic tablets a day. In both cases, stopping garlic fixed the issue.

The chance of serious interaction between garlic and blood thinners is likely low, but caution is still a good idea, especially with high-dose garlic pills.

9. Ginger and Turmeric

Both ginger and turmeric have blood-thinning properties of their own. While they offer anti-inflammatory benefits, consuming large amounts, especially as supplements, can increase your bleeding risk when taken with anticoagulants.

A 36-year-old man who had been on rivaroxaban (Xarelto) for 18 months due to a history of two deep vein thrombosis (DVT) episodes and a Factor V Leiden mutation was admitted to the hospital with coughing up blood (hemoptysis).

He had been stable on treatment with no prior bleeding issues. The only recent change was that he had started drinking 2 to 3 liters of homemade ginger tea daily for about a month.

In another case, a 74-year-old man came to the emergency room with pain in his left thigh and was found to have a large spontaneous hematoma (a big area of internal bleeding). One week before coming to the hospital, he had started taking 1 gram of curcumin daily (a compound found in turmeric).

10. Licorice Root

Licorice root, often found in herbal teas or supplements, may reduce the effects of anticoagulants by blocking clotting proteins like factor Xa and thrombin. It can also increase blood pressure, further complicating cardiovascular care.

A 92-year-old woman with atrial fibrillation was taking phenprocoumon (Marcumar), a type of blood thinner, to prevent strokes. She also had high blood pressure, heart disease, type 2 diabetes, mild dementia, and kidney problems.

Even though her INR levels were in the target range (2-3) in the months before, she suddenly had an ischemic stroke. At the time of the stroke, her INR had dropped to 1.25, which means her blood was not thin enough to prevent clotting.

Looking back, doctors couldn’t find any issues with her medication or behavior, except that she had eaten about 1.5 kg (3.3 lbs) of hard-boiled licorice candy just before the stroke.

11. Tonic Water

Tonic water contains quinine, which may enhance the effects of blood thinners in rare cases. Even in small amounts, quinine can trigger serious side effects in some people, including:

• • Low platelet counts
  • Anemia
  • Kidney damage
  • Bleeding problems

A 35-year-old healthy man came to the emergency room feeling tired, had a fast heartbeat, and was bleeding from his rectum, and had vomited blood. The symptoms started suddenly a few hours earlier. He had no known health issues, no new medications, and no major diet changes.

Doctors learned that he had been drinking only tonic water for 10 days to relieve nighttime leg cramps. His lab tests showed a serious blood condition called disseminated intravascular coagulation (DIC), a life-threatening disorder where the blood overclots and then causes bleeding. After stopping the tonic water, his condition gradually improved.

Note that this man wasn’t even on any anticoagulant medication. For someone who is, the risk of serious bleeding could be significantly higher.

12. Avocados

Avocado flesh is generally safe to eat in moderation while taking warfarin. However, the peel and seed, though not usually consumed, have been found in lab studies to contain phenolic compounds with anti-clotting properties. In tests using human platelets, avocado peel extract reduced platelet aggregation, suggesting a potential blood-thinning effect in concentrated form.

These effects raise a point of caution, especially if you’re taking avocado-based supplements.

13. Berries (in Excess)

While blueberries, strawberries, and raspberries are rich in antioxidants, consuming large amounts could potentially amplify the effect of blood thinners.

In one study, researchers tested different types of strawberry extracts to see if they reduced platelet activity. The strawberries that worked best in the lab were then given to mice to test how well they prevented clotting in live animals.

They found that three types of strawberries had strong antiplatelet effects, both in lab tests and when eaten. Two of them helped prevent clotting, but also slightly impaired blood vessel function. The other type reduced platelet activity without affecting blood vessels.

Strawberries with higher antioxidant levels and more phenolic compounds had stronger anti-clotting effects.

14. Pomegranate Juice

Some evidence suggests that pomegranate juice may interfere with enzymes involved in breaking down blood thinners, similar to the effects seen with cranberry or grapefruit. While research is limited, it’s best to check with your doctor before consuming it regularly.

In animal studies, pomegranate peel extract showed strong blood-thinning properties. It provided up to 80% protection against clot formation in mice. The extract was found to reduce platelet aggregation triggered by various natural clotting agents like ADP, collagen, and thrombin, essentially interfering with the body’s ability to form clots when needed.

Even more concerning, the extract increased bleeding time and prolonged clotting times in rats, which are clear signs of antiplatelet and anticoagulant activity.

Given these findings, pomegranate, especially in concentrated or supplement form, may amplify the effects of anticoagulant medications and increase the risk of bleeding.

15. Clove and Clove Oil

Clove contains eugenol, a compound with natural blood-thinning properties.

In lab studies, it interfered with the body’s natural ability to stop bleeding. In animal experiments, clove oil provided 100% protection against clot formation in one model and 70% in another, which might sound beneficial. However, for someone already on blood thinners, this effect can be excessive and increase the risk of uncontrolled bleeding.

Clove oil also suppressed clot-promoting chemicals, further disrupting normal clotting function.

Even small amounts could potentially enhance the effects of medications like warfarin or apixaban and lead to serious bleeding complications.

16. Fenugreek

Fenugreek, a widely used herb in both cooking and traditional medicine, has been shown to significantly slow blood clotting in lab tests using samples from healthy individuals. The study found that it increased prothrombin time (PT), a key indicator of how long it takes blood to clot, and this effect became more pronounced with higher doses of the extract. In simple terms, fenugreek behaves like a natural blood thinner.

One patient treated with warfarin for atrial fibrillation experienced a sudden increase in her INR, which means her blood was taking too long to clot. After asking about her habits, doctors found she had been taking herbal supplements, including boldo and fenugreek.

When she stopped using the herbs, her INR returned to normal within a week. But a few days later, when she started taking them again, her INR increased again, confirming the herbs were likely responsible.

17. Willow Bark

Willow bark, which comes from the Salix plant, naturally contains salicylates, a group of compounds similar to the active ingredient in aspirin. Because of this, willow bark is often referred to as a natural NSAID (non-steroidal anti-inflammatory drug).

However, it has also been reported to have antiplatelet effects. Extracts of willow bark often contain at least 1% salicylates, and when you take around 240 mg of salicin (one of the main salicylates) daily, it can reach levels in your body that relieve pain, similar to aspirin.

Side effects like those from aspirin, such as stomach irritation or bleeding, can also occur.

18. Evening Primrose Oil

This supplement is popular for hormonal balance and skin health, but it may inhibit platelet aggregation, which can make blood-thinning medications more potent and risky.

Researchers tested how evening primrose oil affects blood clotting activity in rabbits. Results showed that evening primrose oil reduced blood clotting activity and oxidative damage in rabbits fed a high-fat diet. This suggests it may have blood-thinning effects and could influence clotting in humans, too.

19. Red Clover and Dong Quai

Both red clover and dong quai are traditional Chinese herbs often used for menstrual issues and menopause symptoms. They contain coumarin-like compounds that may increase the effects of warfarin and raise the risk of bleeding.

Natural coumarins are a group of plant-derived compounds found in many herbs, spices, fruits, and vegetables. They are not the same as prescription blood thinners, but they share a similar chemical structure and can sometimes affect blood clotting or interact with medications.

A 53-year-old woman had a spontaneous brain bleed (subarachnoid hemorrhage) while taking warfarin along with herbal supplements that contained red clover, dong quai, ginseng, and other ingredients. She had been using them for four months.

20. Lycium

Lycium (commonly known as goji berry) is known for its antioxidant, anti-inflammatory, and possible anti-cancer properties. It’s sometimes used for managing diabetes, high blood pressure, and even erectile dysfunction.

Although lab tests show that Lycium is only a weak inhibitor of the liver enzyme CYP2C9 (which helps break down warfarin), this may still matter in real-life use. In one reported case, a Chinese woman who had stable INR levels while on warfarin experienced a sharp increase in her INR (from 2.0 to 4.1) after drinking 3 to 4 glasses of Lycium tea per day for 4 days. Her INR returned to normal after she stopped the Lycium.

In another case, a 71-year-old woman experienced nosebleeds, bruising, and rectal bleeding after drinking 30 mL of Lycium juice twice daily for 4 days while on warfarin.

In a more recent case, a 65-year-old Chinese man who had been taking warfarin long-term experienced high INR levels and bleeding after drinking goji berry wine.

Large amounts of goji berries (more than 6-12 grams) can intensify the effects of warfarin, raising the risk of bleeding.

Final Thoughts

When you’re on blood thinners, what you eat can affect how well the medicine works. Instead of cutting out lots of foods, try to keep your diet steady, especially with foods high in vitamin K. Avoid making big changes without talking to your doctor first.

Frequently Asked Questions