Nattokinase is not a blood thinner in the traditional pharmaceutical sense, but it does thin blood through several overlapping mechanisms. It breaks down fibrin (the protein mesh that forms blood clots), reduces clotting factors in the bloodstream, and inhibits platelet clumping. The net effect is real anticlotting activity, which is why the distinction between “blood thinner” and “not a blood thinner” matters less than understanding what it actually does in your body.
How Nattokinase Affects Clotting
Prescription blood thinners generally work in one of two ways: they either prevent clots from forming (anticoagulants like warfarin) or they dissolve clots that already exist (fibrinolytics). Nattokinase does both, though through different pathways than pharmaceuticals.
Nattokinase is a serine protease enzyme extracted from natto, a Japanese fermented soybean food. Its primary action is fibrinolytic, meaning it directly breaks apart the fibrin strands that hold clots together. In rat studies, nattokinase dissolved blood clots roughly four times more effectively than plasmin, the body’s own clot-dissolving enzyme. It also stimulates your body to produce more tissue plasminogen activator, a natural protein that activates your internal clot-clearing system.
Beyond clot dissolution, nattokinase lowers circulating levels of fibrinogen, factor VII, and factor VIII, all of which are proteins your body uses to build clots in the first place. That means it doesn’t just clean up existing clots. It also makes new ones less likely to form. Animal research shows nattokinase inhibits platelet aggregation (the clumping of blood cells that starts the clotting cascade), producing effects similar to aspirin but without the gastrointestinal side effects aspirin is known for.
How It Compares to Prescription Blood Thinners
Warfarin, heparin, and newer anticoagulants work by blocking specific steps in the clotting cascade. Aspirin prevents platelets from sticking together. Nattokinase overlaps with all of these categories to some degree, but it is not interchangeable with any of them. It has never been approved as a drug for preventing strokes, treating deep vein thrombosis, or managing atrial fibrillation.
One case report illustrates the danger of treating it as a substitute. A patient with a mechanical heart valve stopped taking warfarin and self-substituted nattokinase long term. The result was a blood clot forming on the valve, causing chest pain and shortness of breath, and ultimately requiring a second open-heart surgery to replace the valve. Nattokinase has measurable blood-thinning properties, but it has not been tested in the clinical scenarios where prescription thinners save lives.
Blood Pressure Effects
Nattokinase also lowers blood pressure modestly. A meta-analysis of randomized controlled trials found that supplementation reduced systolic blood pressure by about 3.5 mmHg and diastolic pressure by about 2.3 mmHg compared to placebo. That’s a small but meaningful shift, roughly equivalent to what you might see from cutting sodium intake. If you already take blood pressure medication, adding nattokinase could push your readings lower than expected.
Dosage Used in Studies
Most clinical trials have used 100 mg per day, standardized to 2,000 fibrinolytic units (FU), typically for eight weeks. This is the dose that has been studied for effects on blood pressure, cholesterol, and clot-related markers. Supplements on the market range from 2,000 to 4,000 FU per capsule, sometimes higher. Because nattokinase is sold as a dietary supplement in the United States, not a drug, there is no FDA-approved dose. Potency can vary between brands since supplements are not held to the same manufacturing standards as pharmaceuticals.
Bleeding Risk and Drug Interactions
The same properties that make nattokinase appealing for cardiovascular health also create a real bleeding risk when combined with other blood-thinning substances. Memorial Sloan Kettering Cancer Center advises that people with clotting disorders or those taking anticoagulants, fibrinolytics, or antiplatelet drugs should avoid nattokinase entirely. Combining it with aspirin may increase the risk of bleeding in the brain.
The interaction with warfarin is particularly complicated. Nattokinase itself has anticlotting effects that could amplify warfarin’s action. But natto, the food it comes from, is rich in vitamin K, which directly counteracts warfarin. The bacteria used in fermentation can also continue producing vitamin K in the gut after consumption. Some purified nattokinase supplements are processed to remove vitamin K, but not all of them. This creates unpredictable effects on warfarin’s effectiveness, pushing it in opposite directions simultaneously.
In safety testing, mice given nattokinase at high concentrations showed no signs of acute bleeding, no deaths, and normal weight gain over a 14-day observation period. Human trials at the standard 2,000 FU dose have not reported significant adverse effects. But these studies were conducted in generally healthy people, not in patients already on blood thinners or with bleeding disorders.
Stopping Before Surgery
Stanford Medicine’s preoperative guidelines list nattokinase among natural supplements that may cause bleeding problems and recommend stopping it seven days before surgery. This is the same timeline applied to vitamin E and most herbal supplements with blood-thinning potential. If you have a procedure scheduled, including dental surgery, let your surgical team know you take nattokinase so they can plan accordingly.
Regulatory Status
In the United States, nattokinase is classified as a dietary supplement. Manufacturers can make structure/function claims (like “supports healthy blood circulation”) but cannot claim it treats or prevents any disease. It has not undergone the rigorous clinical trial process required for FDA drug approval. This doesn’t mean it’s ineffective, but it does mean the evidence base is thinner than what stands behind prescription anticoagulants, and quality control varies across products.