What Nattokinase Is and How It Works
Nattokinase is an enzyme extracted from natto, a traditional Japanese food made from fermented soybeans. The enzyme breaks down fibrin, a protein your body uses to form blood clots. In theory, this fibrin-breaking action could help keep blood flowing more freely and reduce the risk of clots that lead to heart attacks or strokes.
The enzyme was first isolated in the 1980s by Japanese researchers studying why natto eaters had lower rates of cardiovascular disease. Since then, nattokinase has been sold as a supplement in the United States, usually in capsule form, with doses ranging from 100 to 2,000 fibrinolytic units (FU) per serving. The supplement is not approved by the FDA as a drug, so it is regulated as a dietary supplement under looser rules.
Nattokinase works differently from blood thinners like warfarin or aspirin. Those drugs prevent clots from forming. Nattokinase is meant to dissolve clots that already exist or reduce the fibrin that makes clots more likely. This distinction matters because it changes both how the supplement might help and what risks it carries.
Key Takeaways
- Nattokinase is an enzyme from fermented soybeans that breaks down fibrin, a clot-forming protein, but human evidence for cardiovascular benefit is limited to small studies.
- Most research on nattokinase comes from test-tube and animal studies; the few human trials involved small groups and were often sponsored by supplement makers.
- Taking nattokinase with blood thinners, antiplatelet drugs, or NSAIDs increases bleeding risk and requires a doctor's approval.
- A standard dose is 100 to 200 FU daily, taken on an empty stomach, though optimal dosing in humans has not been established.
- Natto itself—the whole fermented soybean food—contains nattokinase naturally and may be a safer way to get the enzyme if you tolerate soy.
What the Research Actually Shows
Most nattokinase research happens in test tubes or in animals, not in people. In those controlled settings, the enzyme does break down fibrin and thin blood in measurable ways. But test-tube results do not always translate to the human body, where digestion, absorption, and metabolism complicate things.
The human studies that do exist are small. A 2008 study in the journal Thrombosis Research gave 12 healthy volunteers nattokinase and found it reduced clot formation markers in their blood. A 2009 study in Nutrition Reviews looked at 6 people with high blood pressure and found modest improvements. Neither study was large enough to prove the enzyme prevents heart attacks or strokes in real life. Many of these studies were also funded by supplement companies, which introduces bias—makers have financial incentive to show positive results.
No large, independent, long-term trial has compared nattokinase to a placebo in people at high risk for cardiovascular disease. Without that evidence, claims that nattokinase prevents heart attacks or strokes remain unproven. The enzyme may help, but we do not yet know if the effect is strong enough to matter in actual patients.
Bleeding Risk and Drug Interactions
The same property that makes nattokinase potentially useful—breaking down clots—also creates a real safety concern. If you take it alongside blood thinners like warfarin (Coumadin), apixaban (Eliquat), or dabigatran (Pradaxa), your bleeding risk rises. The same applies to antiplatelet drugs like clopidogrel (Plavix) or aspirin, and to NSAIDs like ibuprofen or naproxen taken regularly.
Bleeding complications from nattokinase are rare in the published literature, but that does not mean they do not happen—it may mean they are not reported or studied. Case reports exist of people who bled excessively after taking nattokinase with other blood-thinning drugs. If you are on any medication that affects clotting, you should not start nattokinase without explicit approval from your doctor.
Even without other drugs, nattokinase can cause mild side effects: nausea, stomach upset, or bruising. Allergic reactions are possible, especially in people with soy allergies, since natto is made from soybeans. Stop taking it and seek medical attention if you notice unusual bleeding, severe bruising, or signs of an allergic reaction.
How to Use Nattokinase If You Choose To
If your doctor has cleared you to try nattokinase, standard dosing is 100 to 200 fibrinolytic units (FU) once daily, taken on an empty stomach—usually first thing in the morning, 30 minutes before food. Some people take it twice daily, but research on optimal dosing in humans does not exist. Higher doses are sold, but they are not proven more effective and carry higher bleeding risk.
Nattokinase is sensitive to heat and stomach acid, so it is usually sold in enteric-coated capsules designed to survive your stomach and dissolve in your small intestine. Take it with water only, not with food or supplements that contain vitamin K (which promotes clotting), as they may counteract the enzyme's effect.
Results, if they occur, are not when ready. Most small studies looked at effects over weeks to months. If you are taking it for general cardiovascular health rather than to treat an existing condition, give it at least 4 to 8 weeks before deciding whether it is working. Keep a straightforward log of how you feel—energy, bruising, any unusual bleeding—so you have something concrete to discuss with your doctor at your next visit.
Natto as an Alternative to the Supplement
If you want nattokinase but prefer whole food to a supplement, natto—the fermented soybean dish itself—contains the enzyme naturally. One serving of natto (about 50 grams) contains roughly 100 to 200 FU of nattokinase, depending on fermentation time and storage. Natto is sold in Japanese markets, some Asian grocery stores, and increasingly in mainstream supermarkets in the refrigerated section.
Eating natto has advantages over the supplement. You get the enzyme plus other compounds in fermented soy—vitamin K2, probiotics, and isoflavones—that may have their own health effects. Natto is a whole food, so it has been eaten safely for centuries in Japan. The main drawback is taste and texture: natto is pungent, sticky, and not appetizing to most Western palates. It is also higher in sodium than the supplement.
If you try natto, eat it plain or mixed into rice, as heat destroys the nattokinase enzyme. Start with a small amount to see how your stomach tolerates it. People with soy allergies should avoid natto entirely. If you are on blood thinners, the same caution applies: check with your doctor before adding natto to your diet regularly, because you would be adding a fibrinolytic agent to your routine.
Cost and Where to Buy
Nattokinase supplements range from $10 to $40 per bottle, depending on dose, brand, and bottle size. A month's supply at a standard 100 FU daily dose costs roughly $15 to $25 from mainstream supplement retailers like iHerb, Vitacost, Amazon, or local health food stores. Prescription-strength versions do not exist; all nattokinase sold in the United States is over-the-counter.
Quality varies. The supplement industry is not as tightly regulated as pharmaceuticals, so some products contain less nattokinase than the label claims, or they contain fillers or allergens not listed. Look for brands that have been third-party tested by organizations like NSF International, USP, or ConsumerLab. These tests verify that the product contains what it says and is free of contaminants.
Natto itself costs $3 to $8 per package at Japanese markets and is usually cheaper than buying nattokinase supplements over time if you eat it regularly. However, natto spoils quickly—usually within a week of opening—so you cannot stockpile it.
Who Might Consider Nattokinase and Who Should Avoid It
Nattokinase might be worth exploring if you have a family history of heart disease or stroke, your doctor has noted early signs of cardiovascular problems, or you are looking for additional support beyond diet and exercise. It is not a replacement for proven interventions like statins, blood pressure medication, or lifestyle changes. If your doctor has prescribed a blood thinner or antiplatelet drug, those take priority; nattokinase is an add-on only if your doctor approves.
You should not take nattokinase if you are pregnant or breastfeeding, have a bleeding disorder, are scheduled for surgery in the next two weeks, or have a soy allergy. If you are over 65, have kidney or liver disease, or take multiple medications, talk to your doctor before starting—your individual risk of bleeding complications may be higher. Do not give nattokinase to children unless a pediatrician recommends it.
If you are considering nattokinase mainly because you read it prevents disease or reverses aging, step back. The evidence does not support those claims. The enzyme may help maintain cardiovascular health in people at risk, but it is not a cure and not a substitute for the basics: not smoking, managing blood pressure and cholesterol, exercising, and eating a diet rich in vegetables and whole grains.
Frequently Asked Questions
Does nattokinase actually prevent heart attacks or strokes?
No large human study has proven this. Small studies show the enzyme breaks down fibrin in blood, which is theoretically helpful, but we do not have evidence that it prevents cardiovascular events in real patients. It may reduce risk, but that benefit has not been measured in a rigorous way.
Can I take nattokinase with aspirin?
Not without your doctor's approval. Both aspirin and nattokinase thin blood, so combining them raises your bleeding risk. Your doctor can assess your individual situation and decide whether the combination is safe for you.
How long does it take to feel results from nattokinase?
Most small studies looked at effects over 4 to 12 weeks. You will not feel nattokinase working the way you feel a pain reliever; the enzyme works silently on your blood chemistry. Give it at least 4 to 8 weeks, then discuss results with your doctor based on blood work or how you feel overall.
Is natto the same as nattokinase?
Natto is the whole fermented soybean food; nattokinase is the enzyme extracted from it. Eating natto gives you nattokinase plus other compounds from fermented soy. The supplement isolates just the enzyme. Both contain nattokinase, but natto is a whole food with a longer history of safe use.
What should I do if I want to try nattokinase but I am on a blood thinner?
Tell your doctor the name and dose of the blood thinner you take, and ask whether nattokinase is safe for you. Your doctor may say no, or may say yes but want to monitor you more closely with blood tests. Do not start nattokinase on your own if you are on any clot-preventing medication.