Herbal Supplements That Can Interact With Blood Thinners

"Natural" does not mean "safe with everything." If you take a blood thinner, some herbal products can change how it works. That can mean a higher risk of bleeding, or a medicine that protects you less than it should. This guide covers the best-known examples.

First, who this is for

"Blood thinners" include:

• Anticoagulants such as warfarin, apixaban, rivaroxaban, dabigatran and edoxaban
• Antiplatelets such as aspirin and clopidogrel

If you take any of these, check before starting any herbal product.

Herbs and products to be careful with

St John's wort

This is one of the most important to know. It speeds up how the body breaks down many medicines. It can make warfarin work less well, and it is generally advised to avoid it with newer anticoagulants such as apixaban and rivaroxaban, because it can lower their levels. It also interacts with many other medicines, including antidepressants and the contraceptive pill.

Ginkgo biloba

Ginkgo has been linked to bleeding in case reports, especially alongside blood thinners. The evidence is mixed, but the usual advice is caution, particularly with warfarin or antiplatelets.

Garlic supplements (concentrated)

Garlic in food is fine. High-dose garlic supplements may affect platelets and could add to the effect of a blood thinner.

Dong quai and danshen

Both are used in traditional medicine. Dong quai contains coumarin-like compounds, and both have been reported to raise INR and bleeding risk in people on warfarin.

Ginger and turmeric (curcumin), in high doses

Eating them in cooking is not a concern. In concentrated supplement form, they may have a mild effect on platelets. Ask your pharmacist before taking them regularly.

High-dose fish oil

Normal doses are generally fine, but very high doses may slightly increase bleeding tendency. Mention it to your prescriber.

Green tea and vitamin K-rich products

These do not thin the blood. The opposite: vitamin K works against warfarin. A sudden change in how much green tea, leafy greens or vitamin K supplements you consume can change how well warfarin works. The key is to keep your intake consistent.

What to watch for

Contact your doctor promptly if you notice:

• unusual bruising, or bruises that appear without reason
• nosebleeds or bleeding gums that are hard to stop
• blood in urine or stool, or black stools
• very heavy periods
• headaches, dizziness or weakness that are new or severe

Go to emergency care for severe bleeding, a head injury, or sudden severe headache.

What to do

1. Never stop or change your blood thinner on your own. That can be dangerous.
2. Tell your doctor and pharmacist every supplement you take, including herbal teas and products from overseas.
3. Check before you start anything new. Even one product can matter.
4. Plan ahead for surgery or dental work. Many herbal products are stopped before procedures, but the timing depends on the product. Ask your surgeon or pharmacist.
5. Warfarin users: your INR may need more frequent checks after any change.

The bottom line

Many herbs are fine for many people. But if you take a blood thinner, a few popular ones can raise bleeding risk or weaken your medicine. A quick check with a pharmacist is cheap insurance.

Check your own list

Use the free Interaction Checker on VitaGuide to see whether your medicines and herbs may interact, or email our pharmacist to review them.

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This article is general information and not medical advice. It does not replace advice from your own doctor or pharmacist.

Sources to verify before publishing: NIH National Center for Complementary and Integrative Health (NCCIH) pages on St John's wort and ginkgo; product information for warfarin, apixaban and rivaroxaban; a clinical interaction reference such as Stockley's or Natural Medicines.