What supplements should you not take when on blood thinners?

October 8, 2025 •

4 min read

According to a study published in the Journal of the American Geriatrics Society, more than 20% of patients on anticoagulants reported using nutritional supplements that increased bleeding risk. This highlights the critical importance of understanding what supplements should you not take when on blood thinners to ensure your safety.

Quick Summary

Many common herbal and dietary supplements can cause dangerous interactions with blood-thinning medications. Some increase the risk of bleeding, while others may reduce the medication's effectiveness, necessitating careful medical consultation.

Key Points

Increase Bleeding Risk: Supplements like fish oil, vitamin E, garlic, ginkgo biloba, turmeric, and ginger can increase your bleeding risk when combined with blood thinners.
Decrease Effectiveness: Vitamin K supplements and foods can counteract warfarin. St. John's Wort and CoQ10 can also reduce blood thinner efficacy.
Newer vs. Older Blood Thinners: While warfarin is highly sensitive to Vitamin K, newer blood thinners (DOACs) also have significant interactions with supplements like fish oil, ginkgo, and St. John's Wort.
Consult Your Doctor: Always talk to a healthcare provider or pharmacist before starting, stopping, or changing any supplement while on a blood thinner.
Dietary Consistency (for Warfarin): For warfarin, maintaining a consistent daily intake of Vitamin K-rich foods is more important than eliminating them. Avoid sudden, large changes.
Beware of Herbal Remedies: Herbal and over-the-counter supplements are not always regulated and can have strong, unpredictable effects that mimic or counteract blood thinners.

Supplements that Increase Bleeding Risk

Certain supplements possess their own anticoagulant or antiplatelet properties, and when combined with a prescription blood thinner, they can significantly increase the risk of bleeding. This is a particularly dangerous interaction that can lead to severe complications.

Fish Oil (Omega-3 Fatty Acids)

Fish oil and omega-3 supplements are known for their anti-inflammatory and heart-healthy benefits. However, at higher doses, they have a natural antiplatelet effect that can be compounded when taken with prescription blood thinners. This can raise the International Normalized Ratio (INR) for those on warfarin, increasing bleeding risk. For people taking direct oral anticoagulants (DOACs) like Eliquis, combining with fish oil can also elevate bleeding risk. While fish oil is not a substitute for prescription medication, adding it to a treatment plan should only be done under a doctor's supervision.

Vitamin E

High doses of supplemental Vitamin E can amplify the effects of blood thinners, leading to an increased risk of bleeding. As a fat-soluble vitamin, it can affect blood clotting and should be monitored closely. Taking more than 400 IU of Vitamin E per day is particularly risky when on blood thinners.

Garlic

While common in cooking, concentrated garlic supplements can have antiplatelet effects, which can increase the potency of blood thinners like warfarin. This can cause excessive bleeding and should be avoided or used cautiously under a doctor's guidance.

Ginkgo Biloba

Ginkgo biloba is associated with improved circulation and brain health but has known antiplatelet properties. Combining ginkgo with blood thinners, particularly warfarin, can significantly increase the risk of serious bleeding events.

Turmeric (Curcumin)

Curcumin, the active compound in turmeric, has anti-inflammatory and antioxidant properties and acts as an anticoagulant. When taken in concentrated supplement form, it can increase bleeding risk for those on warfarin.

Ginger

Ginger has demonstrated antiplatelet effects in lab studies. Although reports of interaction with blood thinners are less definitive, caution is advised for anyone on anticoagulants, especially when consuming concentrated supplements.

Other Herbal Supplements Increasing Bleeding Risk

Numerous other herbal remedies also carry the potential for dangerous interaction with blood thinners, including:

Feverfew
Dong Quai
Ashwagandha
Chamomile
Danshen (Salvia miltiorrhiza)
Evening Primrose Oil
Fenugreek

Supplements that Decrease Blood Thinner Effectiveness

Some supplements can interfere with how your body processes blood thinners, making the medication less effective. This can put patients at a higher risk for dangerous clots.

Vitamin K

This is a critical interaction, especially for those on warfarin (Coumadin), which works by blocking the action of Vitamin K in the body. A sudden increase in Vitamin K intake from supplements or diet can directly counteract warfarin's effectiveness, promoting clotting. High amounts are found in leafy green vegetables, certain oils, and multivitamins. For warfarin users, consistent dietary Vitamin K intake is more important than avoiding it entirely.

St. John's Wort

Used as a remedy for depression, St. John's Wort can significantly reduce the concentration of warfarin in the blood by speeding up its metabolism. This can make the blood thinner less effective and increase the risk of blood clots.

Coenzyme Q10 (CoQ10)

CoQ10, a popular supplement for heart health, is structurally similar to Vitamin K and may interfere with warfarin activity. It is associated with a decrease in the medication's efficacy.

Green Tea and Ginseng

Both Green Tea and Ginseng contain compounds that can affect blood clotting. For warfarin users, green tea can decrease the drug's effectiveness, while ginseng has been reported to either increase or decrease its activity, creating unpredictable and dangerous fluctuations.

Comparison of Common Supplement Interactions


Supplement	Primary Effect on Blood Thinners	Potential Risk	Interacts with Warfarin?	Interacts with DOACs?
Fish Oil	Increases blood-thinning effect	Bleeding	Yes	Yes
Vitamin E	Increases blood-thinning effect	Bleeding (high doses)	Yes	Yes (high doses)
Garlic	Increases blood-thinning effect	Bleeding	Yes	Yes
Ginkgo Biloba	Increases blood-thinning effect	Bleeding	Yes	Yes
Turmeric (Curcumin)	Increases blood-thinning effect	Bleeding	Yes	Yes
Vitamin K	Decreases blood-thinning effect	Clotting	Yes	No (directly)
St. John's Wort	Decreases blood-thinning effect	Clotting	Yes	Yes
Ginseng	Variable effect	Clotting/Bleeding	Yes	Yes

Important Considerations for All Blood Thinners

Interactions with DOACs

While warfarin is known for its wide range of interactions, newer DOACs (Apixaban/Eliquis, Rivaroxaban/Xarelto) are not immune. Herbal supplements like Ginkgo Biloba, St. John's Wort, and Fish Oil can still alter their effectiveness and increase bleeding risk. Always discuss any supplement with your doctor when taking a DOAC.

Food and Drink Interactions

Certain foods and beverages can also interact with blood thinners.

Cranberry Juice and Grapefruit: Can increase the blood-thinning effect of warfarin and possibly other anticoagulants.
Alcohol: Excessive alcohol consumption can increase the risk of bleeding, especially when on a blood thinner.
Green Tea: Contains Vitamin K and can reduce warfarin's effectiveness, particularly in large quantities.

Navigating Supplementation Safely

Because of the potential for serious or even life-threatening complications, it is crucial to communicate with your doctor and pharmacist before adding any new supplement to your regimen. A study in the British Journal of Clinical Pharmacology highlights the difficulty in predicting supplement-warfarin interactions due to limited research and lack of regulation. Your healthcare team can assess the risks and monitor your blood's clotting ability (e.g., INR tests for warfarin users) to ensure safe and effective treatment.

Conclusion

Taking blood thinners is a critical medical treatment, and understanding the potential interactions with supplements is essential for safety. Many seemingly harmless products can alter the effectiveness of your medication, either increasing the risk of bleeding or, conversely, reducing the anti-clotting effect. Because of the variability and lack of regulation in the supplement industry, a definitive list of absolute 'do not take' items is difficult to maintain. The safest approach is to assume any supplement could interact and always consult your healthcare provider or pharmacist before starting, stopping, or changing any supplement regimen. Open and consistent communication with your medical team is the best way to manage your health safely while on blood thinners.

For more detailed information on supplement interactions, consult reputable sources like ConsumerLab.com.

Frequently Asked Questions

Fish oil (omega-3 fatty acids), especially in high doses, can increase the blood-thinning effect of your medication and raise the risk of bleeding. It is crucial to discuss this with your healthcare provider before starting fish oil supplements, as your blood's clotting ability may need monitoring.

It depends on the multivitamin. If you are on warfarin, you must check the label for Vitamin K, as high doses can interfere with the medication. Your doctor may prefer you take a multivitamin with a low, consistent dose of Vitamin K.

Consuming these in typical food amounts is generally considered safe. The primary risk comes from concentrated, supplemental forms of garlic and ginger, which have much stronger antiplatelet effects. Always inform your doctor about your dietary habits.

For those on warfarin (Coumadin), Vitamin K is an issue because warfarin works by blocking Vitamin K's clotting action. Eating too much or too little Vitamin K can make the warfarin dose less effective or too strong. Newer blood thinners (DOACs) are not affected by Vitamin K intake.

Yes, they do. While they interact differently than warfarin, they are not immune to interactions. Supplements like fish oil, ginkgo biloba, and St. John's Wort can still alter their effectiveness or increase bleeding risk.

Symptoms of increased bleeding risk include unusual or easy bruising, blood in the urine or stool, prolonged bleeding from cuts, or spontaneous nosebleeds. A dangerous decrease in effectiveness can manifest as signs of a new or worsening clot, such as chest pain or swelling.

No, CBD has been shown to interact with warfarin and other blood thinners by inhibiting its breakdown. This can increase the blood-thinning effect and raise the risk of bleeding. You should avoid CBD and consult your doctor.