What It Is
Nattokinase is an enzyme isolated from natto, a traditional Japanese food made by fermenting soybeans with the bacterium Bacillus subtilis var. natto. First described by Japanese researcher Dr. Hiroyuki Sumi in the 1980s, the enzyme is what gives natto its characteristic sticky, stringy texture.
What makes nattokinase interesting is its fibrinolytic activity — the ability to help break down fibrin, the mesh-like protein that forms the structural backbone of blood clots. Because of this, it has been studied as a supplement for cardiovascular and circulatory support. Supplement potency is measured in FU (fibrinolytic units) rather than milligrams alone, which is why a label may list both (e.g., 100 mg = roughly 2,000 FU).
Because nattokinase directly affects how readily blood clots break down, it is one of the more powerful supplements in the circulation category — and one that demands real caution.
Benefits (with mechanism)
Fibrinolysis (clot breakdown). Nattokinase appears to support the body’s own clot-dissolving system by enhancing fibrin degradation and influencing plasmin activity. Laboratory and small clinical studies suggest it may help maintain healthy blood viscosity and circulation, though large, long-term human trials are still limited.
Blood pressure. Several small randomized trials suggest nattokinase may produce a modest reduction in systolic and diastolic blood pressure, possibly through effects on the renin-angiotensin system and improved vascular function. The effect is gentle and not a substitute for blood-pressure medication.
Circulation and blood markers. Some research suggests nattokinase may help support healthy levels of fibrinogen and other clotting factors, and improve markers of blood flow. Evidence here is preliminary, and results vary by study.
It’s worth being honest about the evidence: most human studies are small and short, and product potency varies widely. Treat nattokinase as a supplement that “may” help — not a proven therapy.
How to Take (Dosage)
- Typical dose: 100-200 mg per day, which usually corresponds to 2,000-4,000 FU.
- FU over mg: Because activity matters more than weight, choose a product that clearly states fibrinolytic units (FU). A common research dose is 2,000 FU/day.
- Timing: Once daily. Many people take it in the evening, with or without food. Enteric-coated forms help the enzyme survive stomach acid.
- Start low: Begin at the lower end and stay there for several weeks before considering any increase, and only under medical guidance.
Do not exceed labeled doses in an attempt to “speed up” results — with a fibrinolytic enzyme, more is not safer.
Best Forms
Look for enteric-coated capsules standardized in FU. Enteric coating protects the enzyme from stomach acid so more reaches the intestine intact. Quality matters a great deal here: choose products from reputable brands that provide third-party testing and clearly disclose FU per serving and the source strain.
Eating natto itself is the whole-food route and is common in Japan, but the enzyme content per serving is variable and natto is also rich in vitamin K2, which can interfere with certain blood thinners. Supplements give a more consistent dose but carry the same precautions.
Safety & Side Effects
This is the most important section. Nattokinase’s clot-dissolving action means it carries a significant bleeding risk, and it must be approached conservatively.
- Bleeding risk: May increase the tendency to bleed or bruise. Watch for nosebleeds, unusual bruising, blood in urine or stool, or bleeding that won’t stop — and seek medical care if these occur.
- Surgery and dental work: Stop nattokinase at least 2 weeks before any scheduled surgery or dental procedure to reduce bleeding risk.
- Who should avoid it entirely: anyone with a bleeding disorder (such as hemophilia), active peptic ulcers, recent stroke or a history of hemorrhagic stroke, uncontrolled high blood pressure, or those who are pregnant or breastfeeding (safety has not been established).
- Soy allergy: Nattokinase is derived from fermented soy. People with soy allergy should not use it.
- Mild effects: Some people report digestive upset.
Nattokinase is an adjunct, not a replacement for any prescribed cardiovascular medication. Never stop or adjust a prescription on your own.
Drug Interactions
Because of the bleeding risk, drug interactions are the central safety concern:
- Anticoagulants — warfarin, heparin, and DOACs such as apixaban, rivaroxaban, and dabigatran. Combining these with nattokinase can dangerously increase bleeding. Do not combine without explicit physician supervision.
- Antiplatelets and NSAIDs — aspirin, clopidogrel, ibuprofen, and similar drugs add to bleeding risk.
- Blood-pressure medications — nattokinase may add a small additional lowering effect; monitor for dizziness or low readings.
- Blood-thinning supplements — fish oil, ginger, curcumin, garlic, ginkgo, and high-dose vitamin E can compound the bleeding effect. Be cautious about stacking these.
If you take any medication that affects clotting or blood pressure, talk to your doctor before starting nattokinase.
Bottom Line
Nattokinase is a fermented-soy enzyme with genuinely interesting research behind it for circulation, modest blood-pressure support, and fibrinolysis. A typical dose is 100-200 mg (2,000-4,000 FU) daily, ideally as an enteric-coated, FU-standardized capsule.
But this is not a casual supplement. Its clot-dissolving action means a real, significant bleeding risk — so it must never be combined with blood thinners or antiplatelets without medical supervision, must be stopped at least two weeks before surgery, and is off-limits during pregnancy, with bleeding disorders, after a stroke, or with a soy allergy. Think of it as an adjunct to, never a replacement for, prescribed cardiovascular care. If you’re considering it, the right first step is a conversation with your doctor.