What Is Nattokinase? Benefits, Dosage & Side Effects

Nattokinase is a protein-digesting enzyme extracted from natto, a traditional Japanese food made by fermenting soybeans with the bacterium Bacillus subtilis. It has drawn attention primarily for its ability to break down fibrin, the protein mesh that holds blood clots together, and research over the past two decades has expanded the list of potential cardiovascular benefits to include blood pressure reduction, cholesterol improvement, and even shrinkage of arterial plaque. The science is genuinely promising in some of these areas, though the supplement occupies an unusual space: widely used in parts of East Asia, increasingly popular in the West, yet still without regulatory approval as a drug anywhere.

Where Nattokinase Comes From

Natto has been eaten in Japan for centuries. It is made by steaming soybeans and inoculating them with Bacillus subtilis var. natto, a bacterium classified as generally recognized as safe. During fermentation, the bacteria produce nattokinase as one of many enzymes, and it is considered the most bioactive ingredient in natto from a cardiovascular standpoint.¹ The enzyme was first identified in the 1980s by Japanese researcher Hiroyuki Sumi, who noticed that a piece of natto placed on a blood clot in a petri dish dissolved the clot far more quickly than expected. That observation launched decades of research into whether nattokinase could serve as an oral alternative to conventional clot-dissolving drugs.

The supplement form sold today is typically produced by large-scale fermentation of Bacillus subtilis, then purified and concentrated into capsules or tablets.² You do not need to eat natto itself to get nattokinase, though some people do. The enzyme’s activity is measured in fibrinolytic units (FU), and most commercial supplements are standardized to deliver a specific number of FU per capsule, commonly 2,000 FU per dose.

How Nattokinase Works in the Body

Nattokinase belongs to a class of enzymes called serine proteases, which cut other proteins at specific sites. Its primary claim to fame is fibrinolysis, the breakdown of fibrin clots. Unlike most prescription clot-dissolving drugs, which work through a single pathway by activating a molecule called plasminogen, nattokinase appears to work through multiple routes simultaneously.³ It can directly degrade fibrin on its own. It also boosts the body’s natural clot-clearing system by increasing levels of tissue plasminogen activator (tPA), the enzyme your blood vessel walls produce to keep clots from growing out of control. In one lab study, nattokinase-containing culture solutions raised tPA activity in human vascular endothelial cells to roughly five times the baseline level.⁴

This multi-pathway activity is what makes nattokinase unusual in the world of clot management. Prescription thrombolytics, the drugs given during heart attacks and strokes, are powerful but carry serious bleeding risks and require hospital administration. Nattokinase is far gentler. It is not a substitute for emergency clot-busting drugs, but the fact that it nudges several anti-clotting mechanisms at once rather than slamming one has researchers interested in its potential for prevention and maintenance.

Does It Actually Survive Digestion?

This is a reasonable question, because most enzymes you swallow get dismantled by stomach acid and digestive enzymes long before they reach the bloodstream. Nattokinase, however, shows enough acid stability to retain at least some activity after passing through the stomach. A human pharmacokinetic study found that after a single oral dose of 2,000 FU, nattokinase activity was detectable in the blood from about 2 hours out to at least 8 hours, with some data showing activity as far as 24 hours post-dose.³

That said, the enzyme is sensitive to highly acidic conditions. Research into delivery technologies, such as encapsulating nattokinase in protective coatings, is ongoing precisely because a meaningful fraction of the enzyme is destroyed by stomach acid before it can be absorbed.⁵ Many supplement manufacturers use enteric-coated capsules to address this, though the quality of that coating varies between brands. Taking nattokinase on an empty stomach or between meals is a common recommendation, the idea being that less stomach acid is present to degrade the enzyme, though controlled studies directly comparing fed versus fasted absorption are limited.

Blood Pressure Reduction

Blood pressure is one of the better-studied benefits of nattokinase, and the evidence is fairly consistent. A 2024 meta-analysis pooling data from multiple randomized controlled trials found that nattokinase supplementation lowered systolic blood pressure by about 3.5 mmHg and diastolic blood pressure by about 2.3 mmHg compared with placebo.⁶ Those numbers are modest but meaningful at the population level; reductions of that size, sustained over years, translate into measurable drops in stroke and heart disease risk.

Individual trials tell a similar story. An 8-week randomized trial found that nattokinase reduced systolic blood pressure by about 5.5 mmHg more than placebo.⁷ A separate North American trial found the diastolic reduction was particularly strong in men, dropping from around 86 mmHg at baseline to 81 mmHg after 8 weeks of nattokinase, compared to no change in the placebo group.⁸ The mechanisms behind the blood pressure effect are not fully understood, but they likely involve nattokinase’s ability to thin the blood slightly and reduce factors that promote clotting and vascular stiffness.

To put this in context, the blood pressure reductions seen with nattokinase are smaller than what you would expect from a standard antihypertensive medication, which typically drops systolic pressure by 8 to 15 mmHg. Nattokinase is not going to replace your blood pressure medication, but it might complement lifestyle changes if your numbers are only mildly elevated.

Cholesterol and Arterial Plaque

Nattokinase’s effects on blood lipids have gained attention more recently. The enzyme appears to lower cholesterol through several biochemical routes, including inhibiting the same enzyme targeted by statin drugs and boosting enzymes that help clear fats from the bloodstream.⁹ Large-scale clinical data has confirmed improvements in overall lipid profiles, though the magnitude varies between studies and is generally more modest than what statins achieve.

Perhaps more striking is the evidence on arterial plaque. A clinical study involving over 1,000 participants found that after 12 months of nattokinase use, the thickness of the carotid artery wall decreased from an average of 1.33 mm to 1.04 mm, and plaque size shrank by up to 36%.¹⁰ About two-thirds of participants showed improvement in plaque size, and roughly three-quarters showed improvement in arterial wall thickness. That study was not placebo-controlled, which limits the strength of the conclusion, but the scale of the plaque reduction was large enough to attract serious scientific interest.

The anti-atherosclerotic effect probably reflects a combination of nattokinase’s lipid-lowering properties and its direct fibrinolytic action. Plaques are not just cholesterol deposits; they contain fibrin, inflammatory cells, and other material. An enzyme that degrades fibrin while also improving the lipid environment might chip away at plaques from two directions.

Protection Against Blood Clots

Clot prevention is the original and most researched application of nattokinase. The enzyme’s fibrinolytic activity has been demonstrated repeatedly in lab, animal, and human studies.¹¹ Beyond direct clot dissolution, nattokinase has shown antiplatelet effects, meaning it reduces the tendency of blood cells to clump together and start forming clots in the first place.¹²

There is also research suggesting nattokinase can help prevent deep vein thrombosis, the dangerous blood clots that form in the legs during long periods of immobility such as long flights or hospital stays.¹³ This is one of the more practical applications that supplement users are interested in, particularly frequent flyers and people with sedentary jobs. The evidence here is encouraging but still limited to relatively small studies.

Common Dosage and How Supplements Are Standardized

Most clinical trials have used doses in the range of 2,000 FU per day, which is the amount in most single-capsule supplements. Some studies have used higher amounts, but 2,000 FU is the dose with the most safety and efficacy data behind it. The Japan Nattokinase Association (JNKA), which certifies nattokinase products, recommends 2,000 FU daily as a standard supplemental dose.

Fibrinolytic units measure the enzyme’s ability to break down fibrin under standardized lab conditions. This is a more useful measure than milligrams, because the weight of the capsule contents tells you nothing about enzymatic potency. When shopping for nattokinase, the FU count is what matters. Products that list only milligrams without an FU specification are harder to evaluate. Look for products certified by JNKA or third-party tested for potency, since the supplement market is not tightly regulated and label accuracy varies.

Timing may also matter. Because the enzyme is sensitive to stomach acid, many practitioners suggest taking it on an empty stomach or at least 30 minutes before eating. Some formulations come in enteric-coated capsules designed to bypass the stomach and dissolve in the less acidic environment of the small intestine.

Side Effects and Safety Concerns

For most people, nattokinase at standard doses is well tolerated. The enzyme comes from a food with centuries of dietary history, and clinical trials have not flagged serious adverse effects in healthy participants. The most commonly reported side effects are mild gastrointestinal symptoms like nausea or stomach discomfort.

The real danger of nattokinase lies not in the supplement itself but in how it interacts with other blood-thinning treatments. Because nattokinase has genuine anticoagulant and fibrinolytic activity, combining it with prescription blood thinners like warfarin, heparin, or direct oral anticoagulants creates a risk of excessive bleeding. You should not take nattokinase alongside these medications without medical supervision. The same caution applies to aspirin, clopidogrel, and other antiplatelet drugs.

People with bleeding disorders, anyone scheduled for surgery, and pregnant or breastfeeding women should avoid nattokinase unless specifically cleared by a doctor. If you are on any blood-thinning medication and want to try nattokinase, your physician needs to know, because it could shift your clotting parameters in ways that make your medication dose inappropriate.

A Cautionary Case About Self-Substitution

One published case report illustrates the risks of treating nattokinase as a drug replacement rather than a supplement. A patient who had received a mechanical heart valve, which requires lifelong anticoagulation with warfarin, independently decided to substitute nattokinase for the prescribed medication. After nearly a year, a blood clot formed on the mechanical valve, and the patient required a second open-heart surgery to replace it.¹⁴ The researchers who reported the case strongly discouraged using nattokinase as a replacement for prescription anticoagulants in high-risk situations. Nattokinase has real biological activity, but it does not provide the same level or consistency of anticoagulation that prescription drugs do, and in life-threatening situations, the difference matters enormously.

Combining Nattokinase with Red Yeast Rice

Red yeast rice is another fermented food-derived supplement. It naturally contains monacolin K, a compound chemically identical to the active ingredient in the statin drug lovastatin. Research has explored whether pairing nattokinase with red yeast rice produces stronger cardiovascular effects than either supplement alone, and the results have been fairly clear: the combination is more effective for lipids than nattokinase by itself.

A six-month trial in people with elevated cholesterol found that nattokinase alone produced no significant lipid improvements until month six, while the combination of nattokinase plus red yeast rice lowered total cholesterol by about 25%, LDL cholesterol by 41%, and triglycerides by 15% starting from the first month.¹⁵ A more recent randomized trial in patients with stable coronary artery disease confirmed this pattern, showing the combination was more effective than either supplement alone at reducing triglycerides, total cholesterol, and diastolic blood pressure.¹⁶

This makes intuitive sense: red yeast rice brings a statin-like mechanism, and nattokinase adds fibrinolytic and antiplatelet activity. Together, they hit cardiovascular risk from two angles. If you are considering this combination, though, the same caution applies as with any statin-class compound. Red yeast rice can cause muscle pain, liver enzyme elevation, and other statin side effects, and it interacts with many of the same drugs that statins do. The “natural” label does not exempt it from real pharmacological effects.

What Nattokinase Cannot Do

Social media has pushed nattokinase into conversations it does not belong in. Claims that it degrades spike proteins related to COVID-19 vaccination, reverses vaccine injuries, or cures long COVID circulate widely online but rest on speculation and preliminary cell-culture data, not clinical evidence. No randomized trial has demonstrated any of these effects in humans. Buying nattokinase for these purposes is, at best, a gamble on extrapolations that researchers have not validated.

Similarly, while nattokinase has shown neuroprotective effects in some animal models, claims that it prevents or treats Alzheimer’s disease are premature. The research is in early stages, and the gap between “this enzyme degrades amyloid fibrils in a test tube” and “this supplement prevents dementia in humans” is vast. The cardiovascular benefits are where the human evidence actually lives.

Soy Allergy and Vitamin K Considerations

Because nattokinase is derived from fermented soybeans, people with soy allergies sometimes worry about reactions. Most commercial nattokinase supplements are highly purified, removing the bulk of soy proteins that trigger allergic responses. However, trace amounts can remain, so if you have a confirmed soy allergy, proceed with caution and consult an allergist before taking nattokinase.

A related concern involves vitamin K. Natto, the whole food, is one of the richest dietary sources of vitamin K2. People on warfarin are typically told to keep their vitamin K intake consistent, because the vitamin directly counteracts the drug. Purified nattokinase supplements, however, usually contain little to no vitamin K, since the enzyme is extracted and concentrated away from the other components of natto. Still, if you take warfarin, check with your prescriber and verify that your specific nattokinase product has been tested for vitamin K content. Some lower-quality products may contain residual vitamin K that could interfere with your anticoagulation control.

For people not on warfarin, the vitamin K2 in whole natto is actually considered beneficial for bone health and arterial calcification prevention. This is one reason some supplement companies now sell nattokinase with added vitamin K2 as a cardiovascular and bone health combination product. Whether the added K2 provides clinically meaningful benefits beyond what a standard diet supplies remains an open question.