Nattokinase for Blood Clots

Every year, as many as 900,000 Americans are affected by a blood clot [7], and an estimated 60,000 to 100,000 of them die — which is why interest in nattokinase for blood clots has grown so quickly.

Nattokinase is a fibrinolytic enzyme extracted from natto, a fermented soybean food, and laboratory work shows it can break down fibrin [4] — the protein mesh that holds a clot together. This guide reviews what the human evidence actually supports, where it falls short, and the safety cautions that matter most.

Table of Contents

• What Blood Clots Are — and Why the Stakes Are High
• How Nattokinase Targets Fibrin
• What Human Studies Actually Measured
• Does Nattokinase Prevent Real Clots?
• Safety, Bleeding Risk, and Who Should Be Cautious
• What to Look for in a Nattokinase Supplement
• BioAbsorb Nattokinase Enzyme: A Clinically Aligned Formula
• Frequently Asked Questions
• Conclusion
• Research References

What Blood Clots Are — and Why the Stakes Are High

A blood clot forms when platelets and a protein called fibrin knit together into a plug. That process is life-saving when it seals a wound, but dangerous when a clot forms inside an intact vessel and blocks blood flow. The two most common forms are deep vein thrombosis (DVT), usually in the leg, and pulmonary embolism (PE), where a fragment travels to the lungs. DVT often announces itself with swelling, warmth, and aching in one limb, but it can also develop silently — which is part of what makes it dangerous.

The scale is larger than most people realize. The CDC estimates that up to 900,000 Americans develop venous blood clots each year [7], with 60,000 to 100,000 deaths — and about one in four PE cases gives no warning before sudden death. Roughly 33% of people who have a clot experience a recurrence within a decade, and more than a third of cases trace back to a recent hospital stay or surgery, when long periods of stillness slow blood flow.

The encouraging counterpoint is that as many as 70% of hospital-associated clots are considered preventable [7]. That prevention figure is what drives the interest in enzymes like nattokinase, the supplement at the center of this question. For a plain-language primer, our guide to what nattokinase is covers the basics before we examine the clot-specific evidence here.

How Nattokinase Targets Fibrin

Nattokinase belongs to a family called serine proteases, and its appeal for clot support comes from acting on the same fibrin scaffold the body must clear on its own. In laboratory testing, nattokinase cleaved cross-linked fibrin about 6 times more efficiently than plasmin [2], the enzyme your body uses for the same job, and was roughly 4 times more effective than plasmin at dissolving thrombi in rats.

It also appears to work indirectly. Reviews describe nattokinase increasing tissue plasminogen activator (tPA) and cleaving and inactivating PAI-1 [4] — the main molecule that puts the brakes on your clot-clearing system. The earliest human work, from 1990, found that oral nattokinase raised plasma fibrinolytic activity and tPA [1], and dissolved induced clots in dogs on angiography.

One honest caveat sits underneath all of this: nattokinase is a fairly large protein, and exactly how much survives stomach acid and reaches the bloodstream intact is still an open research question. That uncertainty is precisely why capsule delivery and dose standardization — covered later in this guide — are not marketing details but genuine variables in whether a product behaves like the one in the studies.

These are mechanism findings, not outcome findings — they explain how nattokinase could plausibly influence clotting, not whether it prevents clinical events. We unpack the biochemistry in detail in our companion article on how nattokinase works.

What Human Studies Actually Measured

The best-controlled human trial gave a single 2,000 FU dose to 12 healthy men in a placebo-controlled crossover design [2]. D-dimer rose at 6 and 8 hours, fibrin degradation products rose at 4 hours, factor VIII activity fell, and clotting time lengthened — all statistically significant, yet every measurement stayed within the normal reference range. D-dimer and fibrin degradation products are the fragments left behind when a clot is broken down, so a rise signals more fibrinolytic activity; the fact that the values never left the normal band tells us the shift was real but modest, not drug-strength.

A longer study added duration. Across 45 participants taking 2,000 FU twice daily for two months [3], fibrinogen, factor VII and factor VIII dropped by 9%, 14% and 17% in healthy subjects, with similar declines in higher-risk groups. The catch is the design: it was open-label and self-controlled, with no placebo arm, which limits how much weight the numbers can carry.

Both studies measured clotting-factor surrogates — the blood markers associated with clot risk — rather than counting actual clots. That distinction is the crux of the honest answer about nattokinase for blood clots.

Does Nattokinase Prevent Real Clots?

Only a handful of studies have tracked clot events rather than markers. The most cited is a long-haul flight trial of 204 high-risk passengers [6], where the treatment group had significantly fewer DVT and superficial clot events than placebo. The important limitation: the supplement was a nattokinase-plus-pycnogenol combination, so the trial cannot isolate how much credit nattokinase alone deserves.

Pulling the literature together, a 2023 systematic review of 6 randomized trials and 546 participants [5] concluded that clinical fibrinolytic and antithrombotic data were too sparse to pool meaningfully. The same review noted that one trial in healthy subjects found no detectable effect on several coagulation and fibrinolytic factors at all — a reminder that results vary by population and study design. Memorial Sloan Kettering reaches a similar verdict, noting that nattokinase reduces clot formation in lab and animal models but that human studies remain limited [8].

Researchers have also looked at specific conditions, including DVT specifically and its potential role in stroke prevention, but the same evidence gap applies: the mechanism is promising, the outcome data are thin.

Safety, Bleeding Risk, and Who Should Be Cautious

Short-term trials have reported few adverse effects at the standard 2,000 FU dose, but the same fibrinolytic activity that interests researchers is also the source of risk. Because nattokinase nudges the body toward less clotting, combining it with anticoagulant or antiplatelet drugs such as warfarin, aspirin, or newer agents can increase bleeding risk [9]. A case report describes acute cerebellar hemorrhage in a patient with prior stroke history.

The most instructive caution is about substitution. Memorial Sloan Kettering documents a patient who replaced warfarin with nattokinase after a mechanical valve replacement and later developed valve thrombosis requiring repeat surgery [8], along with a report of fatal internal bleeding in an older adult using it for an irregular heartbeat. Nattokinase is not a replacement for prescribed anticoagulation.

People on blood thinners, with bleeding disorders, scheduled for surgery within two weeks, or who are pregnant or nursing should not start nattokinase without medical approval. Because fibrinolytic supplements can raise surgical bleeding risk, many clinicians advise stopping them at least two weeks before an elective procedure — tell your surgeon and anesthesia team well in advance. Our articles on nattokinase's blood-thinning activity and drug interactions and the full range of side effects go deeper on each scenario.

What to Look for in a Nattokinase Supplement

If you and your clinician decide a nattokinase supplement is appropriate, a few quality markers separate a credible product from a vague one. The first is potency stated in fibrinolysis units: the human research clusters around the 2,000 FU dose used in the controlled trials, so matching that figure keeps a product aligned with the evidence rather than guessing.

Delivery matters too, because nattokinase is a protein that stomach acid can degrade. Look for a capsule designed to release lower in the digestive tract, and check the vitamin K2 status — natto is naturally rich in K2, which can interfere with warfarin, so a K2-free formula is often preferable for anyone managing that interaction. Finally, third-party testing for potency and contaminants is the transparency signal that backs the label up.

BioAbsorb's Nattokinase Enzyme is one example that meets these criteria, supplying the studied dose in a delayed-release veggie capsule.

BioAbsorb Nattokinase Enzyme: A Clinically Aligned Formula

BioAbsorb Nutraceuticals built its Nattokinase Enzyme around the figure that appears most often in the research: 100 mg delivering 2,000 FU of activity per capsule, taken once daily on an empty stomach. The enzyme is housed in a DRcaps delayed-release veggie capsule that helps protect it from stomach acid on the way to the small intestine — without the phthalates and plasticizers found in many enteric coatings.

Two design choices speak directly to the cautions above. The formula is intentionally free of vitamin K2, which matters for anyone already supplementing K2 or managing a warfarin interaction, and every batch is third-party tested for nattokinase potency (at least 2,000 FU), heavy metals, gluten, and microbial contaminants. It is non-GMO, vegetarian, and free of gluten, nuts, eggs, dairy, fish, and shellfish, manufactured in a GMP-certified Canadian facility. A 180-capsule bottle is a six-month supply at around $49.87, which works out to roughly $0.28 a day. None of this makes nattokinase a treatment for any clotting condition — it simply supplies the studied dose in a verified, transparent form for those who have chosen to use it.

Frequently Asked Questions

Can you take nattokinase for blood clots safely?

For generally healthy adults not on blood thinners, short-term trials at 2,000 FU have reported few adverse effects, but safety is very different for anyone on anticoagulants or with bleeding risk. Nattokinase is not a substitute for prescribed clot medication, and documented case reports of serious harm [8] exist when people self-substitute. Talk to your physician before starting.

How much nattokinase do studies actually use?

The most consistent figure across human research is 2,000 FU, used both as a single dose and as a twice-daily regimen over two months in clinical work [3]. FU (fibrinolysis units) measure enzyme activity, which is more meaningful than milligrams alone.

Does nattokinase dissolve clots that already exist?

In lab and animal models it can: oral nattokinase dissolved induced clots in dogs on angiography [1]. In humans, the evidence is limited to marker changes, and nattokinase is not approved to treat an active clot — a suspected DVT or PE is a medical emergency requiring professional care.

Can I take nattokinase with warfarin or aspirin?

Only under medical supervision. Nattokinase can amplify these drugs' effects, and vitamin K2 in some products can also alter warfarin's INR [9] in the opposite direction, making the combined effect hard to predict. This is a conversation for your prescriber, not a do-it-yourself adjustment.

How fast does nattokinase affect clotting markers?

Quickly, at least on paper: in the controlled single-dose trial, clot-breakdown markers shifted between 2 and 8 hours after one 2,000 FU dose [2]. Importantly, all of those changes stayed within the normal range, so the effect is gentle rather than drug-like.

Is natto the same as a nattokinase supplement?

Not quite. Natto is the whole fermented soybean food that nattokinase is extracted from, and it is naturally very high in vitamin K2 — which can work against warfarin. Many supplements remove the K2 to avoid that interaction, so a capsule and a bowl of natto are not interchangeable; our primer on what nattokinase is explains the difference in full.

Conclusion

The honest answer is mixed: nattokinase shows genuine fibrinolytic activity in the lab and shifts clotting markers in small human studies, but the 6 randomized trials pooled to date [5] do not yet prove it prevents real-world clots. If you and your physician decide a clinically dosed enzyme fits your routine, BioAbsorb's Nattokinase Enzyme supplies the studied 2,000 FU per capsule with third-party-verified potency.

Research References

1. Enhancement of the fibrinolytic activity in plasma by oral administration of nattokinase. Acta Haematologica, Vol. 84(3) (1990). Found that oral nattokinase raised plasma fibrinolytic activity and tPA in humans and dissolved induced thrombi in dogs — the foundational evidence that orally taken nattokinase reaches the circulation.
2. A single-dose of oral nattokinase potentiates thrombolysis and anti-coagulation profiles. Scientific Reports, Vol. 5 (2015). A placebo-controlled crossover in 12 healthy men showing that a single 2,000 FU dose shifted clot-breakdown and clotting-time markers, all within the normal range.
3. Nattokinase decreases plasma levels of fibrinogen, factor VII, and factor VIII in human subjects. Nutrition Research, Vol. 29(3) (2009). An open-label, self-controlled trial in 45 subjects reporting 9–17% reductions in key clotting factors over two months.
4. Nattokinase: A Promising Alternative in Prevention and Treatment of Cardiovascular Diseases. Biomarker Insights, Vol. 13 (2018). A mechanistic review describing fibrin cleavage, tPA enhancement, and PAI-1 inactivation, while noting that clinical evidence is not yet conclusive.
5. Nattokinase Supplementation and Cardiovascular Risk Factors: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Reviews in Cardiovascular Medicine, Vol. 24(8) (2023). Pooled 6 RCTs (546 participants) and concluded clinical fibrinolytic and antithrombotic data were too sparse for firm conclusions.
6. Prevention of Venous Thrombosis in Long-Haul Flights with Flite Tabs: The LONFLIT-FLITE Randomized, Controlled Trial. Angiology, Vol. 54(5) (2003). A 204-passenger RCT showing fewer clot events with a nattokinase-plus-pycnogenol combination, which prevents attributing the benefit to nattokinase alone.
7. Data and Statistics on Venous Thromboembolism. U.S. Centers for Disease Control and Prevention (CDC). Source for the scale of blood-clot incidence, mortality, recurrence, and preventability in the United States.
8. Nattokinase — Integrative Medicine Monograph. Memorial Sloan Kettering Cancer Center (2022). A balanced clinical overview confirming lab and animal antithrombotic activity, limited human data, and documented serious adverse events.
9. Nattokinase — Natural Products Database. Drugs.com. A professional reference covering bleeding-risk case reports, anticoagulant interactions, and Health Canada's 2012 concern about vitamin K2 removal.

About the Author

David Kimbell is a health writer, digital entrepreneur and former aerospace engineer, based in Ottawa, Canada. He loves translating complex science into clear, actionable guidance for consumers seeking evidence-based solutions.

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Important Disclaimers

Medical Disclaimer: This article provides educational information only and is not intended as medical advice. Always consult with a qualified healthcare provider before starting any new supplement, especially if you have existing health conditions, take medications, or are pregnant or nursing.

FDA/Health Canada Statement: These statements have not been evaluated by the Food and Drug Administration or Health Canada. This product is not intended to diagnose, treat, cure, or prevent any disease.