Dong Quai and Warfarin: What You Need to Know About the Bleeding Risk

When you're on warfarin, even small changes in your diet or supplements can throw your blood clotting off balance. One of the most dangerous but often overlooked combinations is Dong Quai and warfarin. This herbal remedy, used for centuries in Chinese medicine to ease menstrual pain and menopause symptoms, can dramatically increase your risk of serious bleeding when taken with warfarin. It’s not a rumor. It’s not speculation. It’s documented in medical guidelines, case reports, and hospital protocols.

What Is Dong Quai, Really?

Dong Quai, also known as Angelica sinensis, isn’t just another herbal tea. It’s a root used in Traditional Chinese Medicine for over 2,000 years. Women in China have used it for generations to manage periods, hot flashes, and hormonal shifts. Today, it’s sold in health food stores across the U.S. as capsules, teas, and tinctures. Many assume it’s safe because it’s "natural." But "natural" doesn’t mean harmless-especially when you’re on a blood thinner.

Dong Quai contains compounds like ferulic acid and osthole, which interfere with platelet function. In simple terms, they make your blood less likely to clot. That sounds helpful if you’re prone to clots-but when you’re already taking warfarin, it’s like stepping on the gas pedal while your brakes are already pressed.

How Warfarin Works-and Why It’s So Sensitive

Warfarin is one of the most prescribed anticoagulants in the world. Over 30 million prescriptions are filled in the U.S. every year. It works by blocking vitamin K, which your liver needs to make clotting factors. Too little, and you bleed. Too much, and you clot. The goal is to keep your INR (International Normalized Ratio) between 2 and 3 for most conditions. That’s a narrow window. A single point above 4 can mean internal bleeding. A point below 2 means your clot risk goes up.

Unlike newer blood thinners like apixaban or rivaroxaban, warfarin’s effects are highly sensitive to what you eat, drink, and take as supplements. Even small changes in your routine can cause your INR to swing. And Dong Quai is one of the top herbal offenders.

The Science Behind the Interaction

The interaction isn’t just theoretical. Multiple studies show Dong Quai doesn’t just add to warfarin’s effect-it multiplies it. A 2015 review in the British Journal of Clinical Pharmacology found Dong Quai inhibits platelet aggregation, meaning it stops blood cells from sticking together. That’s the same mechanism warfarin uses, just through a different pathway. Together, they create a double hit.

Some research suggests Dong Quai may also slow down how quickly your body breaks down warfarin. It appears to inhibit liver enzymes (CYP2C9 and CYP3A4) that metabolize the drug. If your body can’t clear warfarin fast enough, levels build up. Your INR climbs. And you’re at risk.

A 2014 study published in PMC showed that in animal models, Dong Quai significantly increased prothrombin time-meaning it took longer for blood to clot-without changing warfarin blood levels. That’s a clear sign of a pharmacodynamic interaction: the two drugs work together to amplify the effect, even if one isn’t increasing the other’s concentration.

Real Cases, Real Risks

There aren’t dozens of case reports, but the ones that exist are alarming. One 72-year-old woman in Malaysia went to the ER after her INR jumped from 2.8 to 5.1 after starting Dong Quai for menopausal symptoms. She had no history of bleeding, no other changes in meds or diet. Just Dong Quai. She was hospitalized for observation and required a dose reduction of warfarin.

Online forums like Reddit’s r/anticoagulants have over 17 user reports since 2023 of unexplained INR spikes tied to Dong Quai use. HealthUnlocked forums recorded 23 cases between 2020 and 2023 where patients saw an average INR increase of 1.7 points after starting the herb. That’s enough to push someone from a safe range into the danger zone.

And here’s the scary part: 68% of warfarin users don’t even know herbal supplements can interfere with their medication, according to a 2022 survey by the National Center for Complementary and Integrative Health.

What the Experts Say

Major medical institutions don’t mince words:

• The Cleveland Clinic says: "Avoid Dong Quai in warfarin-treated patients due to lack of data."
• The University of California San Diego lists Dong Quai under "Increased Risk of Bleeding," alongside ginkgo, garlic, and fish oil.
• The Memorial Sloan Kettering Cancer Center warns patients to "consult with their physicians before using this herb," especially if they have hormone-sensitive cancers, because Dong Quai also has estrogen-like effects.
• The American Heart Association classifies Dong Quai as a "high-risk herb" for anticoagulant users.

Dr. Catherine Ulbricht, a leading pharmacist at Massachusetts General Hospital, put it bluntly: "The additive antiplatelet effects of Dong Quai could push a patient’s INR from a therapeutic range of 2.5 to potentially dangerous levels above 4.0."

And she’s right. The annual risk of major bleeding for someone on warfarin is already 1.5-2.5%. Add Dong Quai, and that risk doesn’t just go up-it could double.

Why You Can’t Trust the Label

Here’s another hidden danger: Dong Quai supplements aren’t regulated like drugs. The FDA doesn’t test them for purity, potency, or consistency. A 2020 study by the United States Pharmacopeia found that Dong Quai products varied by up to 8-fold in their active ingredient content. One bottle might have enough ferulic acid to affect your INR. The next bottle from the same brand might have almost none.

That’s why you can’t say, "I took it last week and nothing happened, so it’s fine." Each batch is different. Each person reacts differently. There’s no safe dose you can reliably predict.

What Should You Do?

If you’re on warfarin:

1. Stop taking Dong Quai. Even if you feel fine. Even if your doctor didn’t mention it.
2. Tell your doctor. Don’t assume they know you’re taking it. Many patients don’t volunteer supplement use because they think it’s "not medicine."
3. Get your INR checked. If you’ve taken Dong Quai in the last 2 weeks, ask for a test. It takes 3-5 days for the herb’s effects to show in your blood.
4. Ask about alternatives. If you’re using Dong Quai for hot flashes or cramps, ask your doctor about FDA-approved options like low-dose SSRIs, gabapentin, or non-herbal hormonal therapies.

If you’re not on warfarin but considering Dong Quai:

• Ask your doctor if you’re taking any other blood thinners, aspirin, NSAIDs, or supplements like fish oil or garlic.
• Don’t assume "natural" means safe. Many herbs are more potent than people realize.

What About Other Herbs?

Dong Quai isn’t alone. At least 90 Chinese herbal medicines have documented interactions with anticoagulants. Ginkgo, garlic, ginger, turmeric, and ginseng all carry similar risks. In fact, warfarin has more documented herb interactions than any other blood thinner.

And it’s not just Chinese herbs. Even common ones like St. John’s wort can interfere with warfarin metabolism. The bottom line? If you’re on warfarin, assume every supplement is a potential risk until proven otherwise.

What’s Changing?

Regulators are catching up. The European Medicines Agency now requires Dong Quai product labels in EU countries to include a warning about warfarin interactions, effective January 2025. The NIH is funding a major clinical trial at the University of Illinois to study this interaction in humans-results are expected in late 2024.

But until then, the advice remains simple: don’t take Dong Quai if you’re on warfarin. There’s no benefit worth the risk.

Final Thought: Natural Doesn’t Mean Safe

It’s easy to believe that if something’s been used for centuries, it must be harmless. But medicine has evolved. We now know how drugs work at the molecular level. We know how herbs interact with them. And we know that when you mix Dong Quai and warfarin, you’re playing with fire.

Your health isn’t a gamble. Don’t risk bleeding, hospitalization, or worse because you didn’t ask the right question. Talk to your doctor. Get your INR checked. And if you’re taking Dong Quai-stop. Your blood will thank you.