Nattokinase and Blood Thinners: Is It Safe to Combine? (2026)

At a Glance

• Short answer Don’t combine nattokinase with a blood thinner on your own. Memorial Sloan Kettering (MSK) advises people taking anticoagulants or daily aspirin not to use it¹.
• Why Nattokinase affects clotting. It lengthened clotting tests in a placebo-controlled trial⁵, and bleeding in the brain was reported in a man who took it with aspirin².
• Never use it instead of a blood thinner A patient who replaced warfarin with nattokinase developed a clot on a mechanical heart valve⁴.
• Warfarin and natto Natto, the food, is rich in vitamin K and can block warfarin’s effect⁸⁹.
• If your doctor approves it anyway Expect closer monitoring. The only study of combined use was done in a hospital with careful follow-up⁷.

The Short Answer: It isn’t considered safe to combine nattokinase with blood thinners without medical supervision. Nattokinase breaks down fibrin and lengthens clotting times⁵⁶, so taking it with warfarin, a newer anticoagulant, aspirin or clopidogrel could add to your bleeding risk. MSK lists anticoagulant and antiplatelet drugs as possible interactions and advises people on them not to use nattokinase¹.

On this page

1. Nattokinase and Blood Thinners: Medicine by Medicine
2. Why the Combination Is Risky
3. What Case Reports Show
4. Warfarin, Natto and Vitamin K
5. Before Surgery or Dental Work
6. If Your Doctor Approves Nattokinase
7. Final Verdict
8. Frequently Asked Questions

There are no controlled trials of nattokinase with most blood thinners, so the warning is based on how it works, clotting tests and case reports. For an overview of all its risks, see our guide to nattokinase side effects.

Nattokinase and Blood Thinners: Medicine by Medicine

Medicine	Possible interaction	Evidence
Warfarin (Coumadin, Jantoven)	Added bleeding risk; natto’s vitamin K can also weaken warfarin18	Theoretical + food studies
Apixaban (Eliquis), rivaroxaban (Xarelto), dabigatran (Pradaxa), edoxaban	May increase bleeding risk1; supplement interactions with these drugs are poorly studied11	Theoretical
Aspirin	Bleeding in the brain reported with combined use2; MSK advises daily aspirin users to avoid nattokinase1	Case report
Clopidogrel (Plavix) and other antiplatelet drugs	May increase bleeding risk1	Theoretical
Heparin, enoxaparin, fondaparinux	Used together only under hospital monitoring in one study7	Observational
Clot-dissolving drugs	May increase bleeding risk1	Theoretical

“Theoretical” means the risk is based on how nattokinase works and on clotting tests, not on trials in people taking these drugs. That’s a reason for caution, not reassurance.

Why the Combination Is Risky

Blood thinners work in different ways: warfarin and the newer anticoagulants slow the formation of clots, while aspirin and clopidogrel make platelets less sticky. Nattokinase works on another part of the process, helping break down fibrin in clots that have already formed¹.

In studies, nattokinase:

• Lengthened clotting tests (aPTT and a platelet test) over 8 weeks compared with placebo⁵.
• Raised markers of clot breakdown and briefly lengthened clotting time after a single 2,000 FU dose in healthy men, though values stayed in the normal range⁶.

Adding a second product that affects clotting to a blood thinner makes the overall effect harder to predict.

What Case Reports Show

• Aspirin: A man taking aspirin to prevent another stroke had bleeding in the cerebellum after taking 400 mg of nattokinase a day for 7 days. His MRI also showed many small old bleeds, which may have made him more vulnerable².
• No other blood thinner: An elderly woman taking an over-the-counter nattokinase supplement developed bleeding into her abdomen and died³.
• Replacing warfarin: A patient with a mechanical aortic valve stopped warfarin and took nattokinase instead. Nearly a year later, a clot formed on the valve and the valve had to be replaced again⁴.

Case reports can’t prove cause and effect, but they show the kinds of harm doctors worry about.

Warfarin, Natto and Vitamin K

Natto, the fermented soybean food, is high in vitamin K2. Eating it raised vitamin K in the blood and blocked warfarin’s effect in patients after heart valve surgery⁸, and people on warfarin are told to avoid it⁹. MSK notes this as a separate reason for warfarin users to be careful¹.

Nattokinase supplements are different from the food, and some nattokinase ingredients have had vitamin K2 removed¹⁰. Even so, a product without vitamin K still affects clotting⁵, so the bleeding concern remains.

Before Surgery or Dental Work

Because nattokinase changes clotting tests⁵, tell your surgeon, dentist and anesthesiologist if you take it. Ask how long before the procedure you should stop.

If Your Doctor Approves Nattokinase

Some doctors may allow it in specific situations. In the only study of combined use, patients took nattokinase with injected blood thinners while in vascular surgery care, and the authors stressed close monitoring, including INR checks and dose adjustments⁷. If your doctor agrees to a trial of nattokinase:

1. Don’t change your blood thinner dose on your own.
2. Expect more frequent blood tests, especially INR if you take warfarin.
3. Tell every doctor and pharmacist you take nattokinase.
4. Watch for warning signs: unusual bruising, nosebleeds, bleeding gums, blood in your urine or stool, black stools, a severe headache or sudden weakness. Get emergency care for a severe headache or weakness on one side.

For what nattokinase can and can’t do, see our guide to nattokinase benefits. If you aren’t on any blood thinner and are comparing products, see our guide to the best nattokinase supplements.

Final Verdict

Nattokinase and blood thinners shouldn’t be combined without your doctor’s approval and monitoring. Nattokinase measurably affects clotting, serious bleeding has been reported with aspirin, and MSK advises people on anticoagulants or daily aspirin to avoid it. Never stop a prescribed blood thinner to take nattokinase instead.

Important: This guide is for general information and isn’t medical advice. Don’t start, stop or change a blood thinner or add nattokinase without talking to the doctor who prescribed it. Seek emergency care for a severe headache, weakness on one side, or heavy bleeding.

Frequently Asked Questions

Sources & History11 sources · updated November 11, 2026

References

1. Nattokinase — Memorial Sloan Kettering Cancer Center, About Herbs, 2025
2. Cerebellar Hemorrhage Provoked by Combined Use of Nattokinase and Aspirin in a Patient With Cerebral Microbleeds — Internal Medicine, 2008
3. Nattokinase-Associated Hemoperitoneum in an Elderly Woman — Cureus, 2021
4. Consequence of Patient Substitution of Nattokinase for Warfarin After Aortic Valve Replacement With a Mechanical Prosthesis — Proceedings (Baylor University Medical Center), 2015
5. The Effects of Nattokinase Supplementation on Collagen-Epinephrine Closure Time, Prothrombin Time and Activated Partial Thromboplastin Time in Nondiabetic and Hypercholesterolemic Subjects — Food & Function, 2019
6. A Single-Dose of Oral Nattokinase Potentiates Thrombolysis and Anti-Coagulation Profiles — Scientific Reports, 2015
7. Data Recorded in Real Life Support the Safety of Nattokinase in Patients With Vascular Diseases — Nutrients, 2021
8. Warfarin Antagonism of Natto and Increase in Serum Vitamin K by Intake of Natto — Artery, 1990
9. First Clinical Trial of a Newly Developed, Low Menaquinone-7, Fermented Soybean Natto in Warfarin-Dependent Patients — Journal of Medicinal Food, 2021
10. Consumption of Nattokinase Is Associated With Reduced Blood Pressure and von Willebrand Factor: Results From a Randomized, Double-Blind, Placebo-Controlled, Multicenter North American Clinical Trial — Integrated Blood Pressure Control, 2016
11. The Clinical Significance of Drug-Food Interactions of Direct Oral Anticoagulants — International Journal of Molecular Sciences, 2021

Update history

• November 11, 2026Rewritten with a medicine-by-medicine interaction table graded by evidence, case reports, natto and vitamin K data for warfarin users, a hospital study of combined use, and monitoring guidance.