- Nattokinase is a fibrinolytic enzyme extracted from natto, a fermented soybean food traditional to Japan, sold in enteric-coated capsules dosed in fibrinolytic units (FU), typically 2,000 FU/day.
- The viral claim that nattokinase "dissolves clots" or "microclots" and reverses Long-COVID is Insufficient in humans — it rests almost entirely on in-vitro (test-tube) fibrin-degradation assays, not clinical trial outcomes.
- A more modest, better-supported claim — that nattokinase lowers blood pressure — is graded Moderate, based on a meta-analysis of 6 RCTs and an independent 8-week RCT, both showing small but statistically significant reductions in systolic and diastolic blood pressure.
- Safety-critical: nattokinase carries a real bleeding risk. It should not be combined with anticoagulants (warfarin, DOACs) or antiplatelets (aspirin, clopidogrel) without medical supervision, and should be stopped before surgery.
- Because it is derived from natto, some nattokinase products carry variable amounts of vitamin K2, which can itself interact with warfarin — a separate interaction wrinkle from the enzyme's own fibrinolytic action.
- Nattokinase is sold in the US as an unapproved dietary supplement, not an FDA-approved drug; it carries no approved claim to treat, dissolve, or prevent blood clots.
Table of contents
- Evidence summary
- What nattokinase is
- All forms and grades
- How it works
- The hype vs the evidence
- Benefits by claim
- What works and what does not
- Risks and all side effects
- All interactions
- Who should avoid nattokinase
- Dosage and how to take
- Animal and in-vitro evidence excluded
- Independent funding and conflict notes
- Frequently asked questions
- Sources and funding notes
Evidence summary
| Claim | Evidence | Source | Funding/conflict | Strength |
|---|---|---|---|---|
| Lowers blood pressure | Meta-analysis of 6 RCTs (n=546): systolic BP reduced by mean difference −3.45 mmHg (95% CI −4.37 to −2.18); diastolic BP reduced by −2.32 mmHg (95% CI −2.72 to −1.92) | Li 2023, Rev Cardiovasc Med | Academic (Henan University of Chinese Medicine); no manufacturer funding disclosed | Moderate |
| Lowers blood pressure (single RCT) | RCT, 86 pre-/stage-1 hypertensive adults, 8 weeks: 2,000 FU/day cut systolic BP by −5.55 mmHg and diastolic BP by −2.84 mmHg vs. control, with reduced plasma renin activity | Kim 2008, Hypertens Res | Academic (Yonsei University); independent | Moderate |
| Lipid effects (cholesterol/triglycerides) | Inconsistent, dose-dependent effects across pooled RCTs; small rise in blood glucose observed | Li 2023, Rev Cardiovasc Med | Academic; independent | Weak |
| "Dissolves" blood clots / microclots in the body | No adequate human RCT outcome data; evidence is fibrinaloid-microclot degradation in laboratory blood-sample (in-vitro) assays only | Liverpool preprint, 2024; bioRxiv preprint, 2024 | Academic preprints; in-vitro, not peer-reviewed clinical trials | Insufficient (in-vitro only, excluded from clinical conclusions) |
| Long-COVID "de-clotting" / symptom relief | No published human RCT evidence; claim is extrapolated from in-vitro fibrin-plate assays and product marketing content | RTHM supplement guide | Clinic/product-adjacent content; not an independent trial | Insufficient |
| General cardiovascular/thrombosis prevention claim | No large-scale human clinical endpoint trials (e.g., stroke, MI, DVT incidence) exist for nattokinase | See mechanism section | N/A | Insufficient |
What nattokinase is
Nattokinase is a fibrinolytic serine protease (a subtilisin-family enzyme) extracted from natto, a traditional Japanese food made by fermenting soybeans with the bacterium Bacillus subtilis var. natto. It is not a vitamin or mineral — it is an enzyme, isolated and concentrated from the fermentation process, then formulated into dietary supplements rather than eaten as whole natto. Interest in the ingredient has grown sharply, with search momentum up roughly 173% year over year, driven largely by a viral "microclot" narrative connected to Long-COVID recovery communities (Rising Trends 2026; RTHM).
In the supplement aisle, nattokinase is almost always sold as an enteric-coated capsule — the coating is intended to protect the enzyme from being broken down by stomach acid before it reaches the small intestine for absorption. Potency is not measured in milligrams alone but in fibrinolytic units (FU), a measure of the enzyme's clot-degrading activity in laboratory assays. The most common commercial dose is 2,000 FU per day, roughly equivalent to 100 mg of standardized extract (Li 2023, Rev Cardiovasc Med). A highly purified, standardized version called NSK-SD is widely used in both commercial products and in several of the clinical trials described below.
All forms and grades
| Form | Description | Standardization | Typical source |
|---|---|---|---|
| Enteric-coated capsules | The dominant commercial form; coating intended to survive stomach acid before releasing the enzyme in the intestine | Dosed in fibrinolytic units (FU), commonly 2,000 FU/day (~100 mg) | Li 2023, Rev Cardiovasc Med |
| NSK-SD (branded purified extract) | A specific, highly purified nattokinase preparation used in commercial products and cited in clinical/marketing literature | Standardized to FU activity | RTHM supplement guide |
| Whole natto (food) | The original fermented soybean food; contains nattokinase plus natural vitamin K2 and other fermentation byproducts | Not standardized; enzyme activity and vitamin K2 content vary by batch and fermentation method | WebMD monograph |
| Powder/loose extract | Less common than capsules; typically used in bulk supplement manufacturing rather than direct-to-consumer sale | Variable FU labeling | Li 2023, Rev Cardiovasc Med |
How it works
Nattokinase's proposed mechanism is that, as a serine protease, it directly degrades fibrin — the structural protein that forms the mesh of a blood clot — and may also promote the body's own clot-dissolving system by influencing plasminogen activators and reducing plasminogen activator inhibitor activity. In the blood-pressure trials, one proposed mechanism is a reduction in plasma renin activity, part of the renin-angiotensin system that regulates blood vessel constriction (Kim 2008, Hypertens Res).
The direct "clot-dissolving" mechanism — the basis of the viral microclot claim — has been demonstrated almost exclusively in IN-VITRO (non-human) evidence: laboratory assays where nattokinase is added directly to blood plasma or fibrin plates outside the body and degradation of the fibrin structure is observed under a microscope (Liverpool preprint, 2024; bioRxiv, 2024). This kind of test-tube result cannot establish that an orally ingested capsule survives digestion, is absorbed intact in meaningful quantities, circulates to a clot site, and produces the same effect inside a living person. No human trial has demonstrated that oral nattokinase dissolves existing clots or microclots in the body. This distinction — a plausible laboratory mechanism versus a proven clinical effect — is the central gap between the hype and the evidence for nattokinase.
The hype vs the evidence
The viral pitch for nattokinase, amplified across wellness and Long-COVID social media, is that it "dissolves clots and microclots," reverses fibrinaloid microclot buildup blamed for lingering Long-COVID symptoms, and lowers blood pressure — essentially positioning it as a natural blood thinner and circulation fix (RTHM).
What the human evidence actually shows on blood pressure: a systematic review and meta-analysis of 6 randomized controlled trials (546 participants) found nattokinase produced a real but modest reduction in blood pressure — systolic blood pressure down by a mean difference of 3.45 mmHg (95% CI −4.37 to −2.18) and diastolic blood pressure down by 2.32 mmHg (95% CI −2.72 to −1.92) (Li 2023, Rev Cardiovasc Med). An independent 8-week RCT in 86 people with pre-hypertension or stage-1 hypertension found a similarly modest drop of 5.55 mmHg systolic and 2.84 mmHg diastolic at 2,000 FU/day (Kim 2008, Hypertens Res). These are real, statistically significant effects — but they are in the same modest range as lifestyle interventions like reduced sodium intake, not a dramatic cardiovascular fix.
What the human evidence shows on "dissolving clots/microclots" and Long-COVID: essentially nothing at the clinical trial level. No randomized controlled trial has tested whether oral nattokinase reduces microclot burden, improves Long-COVID symptoms, or lowers rates of stroke, heart attack, or deep vein thrombosis in humans. The entire mechanistic case rests on in-vitro fibrin-plate assays showing the enzyme degrades fibrin structures in blood samples in a lab setting (Liverpool preprint, 2024; bioRxiv, 2024). This evidence is explicitly excluded from any clinical claim in this article because it cannot show that the enzyme reaches or clears clots inside a living person. The gap between "we watched it dissolve fibrin in a dish" and "it treats Long-COVID" is the single most important thing for a consumer to understand before buying this supplement for that purpose.
Effect sizes at a glance
| Outcome | Effect size | Duration/dose | Source |
|---|---|---|---|
| Systolic BP (meta-analysis) | −3.45 mmHg (95% CI −4.37 to −2.18) | Pooled across 6 RCTs, 546 participants | Li 2023 |
| Diastolic BP (meta-analysis) | −2.32 mmHg (95% CI −2.72 to −1.92) | Pooled across 6 RCTs, 546 participants | Li 2023 |
| Systolic BP (single RCT) | −5.55 mmHg vs. control | 2,000 FU/day for 8 weeks | Kim 2008 |
| Diastolic BP (single RCT) | −2.84 mmHg vs. control | 2,000 FU/day for 8 weeks | Kim 2008 |
| Microclot/fibrin degradation | Not quantifiable in a human clinical sense — in-vitro only | Laboratory blood-sample assay, not a dosing trial | bioRxiv, 2024 |
Benefits by claim
Blood pressure
This is nattokinase's best-supported claim. Both an independent meta-analysis of 6 RCTs and an independent standalone RCT found small but statistically significant reductions in systolic and diastolic blood pressure at doses around 2,000 FU/day, with one trial linking the effect to reduced plasma renin activity (Li 2023, Rev Cardiovasc Med; Kim 2008, Hypertens Res). Grade: Moderate.
Cholesterol and lipid profile
Pooled trial data show inconsistent, dose-dependent effects on lipids, alongside a small increase in blood glucose in some trials — not a clear or reliable benefit (Li 2023, Rev Cardiovasc Med). Grade: Weak.
"Dissolving" clots and microclots
No human clinical trial has tested or confirmed this claim. The entire evidentiary basis is in-vitro fibrin-degradation assays performed on blood samples in a lab, not in living people (Liverpool preprint, 2024; bioRxiv, 2024). Grade: Insufficient.
Long-COVID and "microclot" symptom relief
There is no published human RCT evidence that nattokinase improves Long-COVID symptoms or reduces circulating microclots in patients. The narrative is built on in-vitro assay results and patient-community/product-marketing content, not controlled clinical outcomes (RTHM). Grade: Insufficient.
General thrombosis/stroke prevention
No large human clinical-endpoint trials (stroke, heart attack, DVT incidence) exist for nattokinase. Extrapolating from a laboratory fibrinolytic mechanism to real-world clot prevention is not supported by current human evidence. Grade: Insufficient.
What works and what does not
| Claim | Verdict | Why |
|---|---|---|
| Modestly lowers blood pressure | Moderate support | Consistent small reductions across an independent meta-analysis and an independent RCT (Li 2023; Kim 2008) |
| Improves cholesterol/lipids | Not reliable | Inconsistent, dose-dependent results across pooled trials (Li 2023) |
| Dissolves existing blood clots in the body | Not established | Only shown in-vitro; no human clinical outcome data |
| Reverses Long-COVID microclots/symptoms | Not established | No human RCTs; claim rests on in-vitro assays and marketing content |
| Safe to combine freely with blood thinners | False / unsafe | Documented additive bleeding risk (MSKCC) |
Risks and all side effects
| Side effect | Frequency/severity | Notes |
|---|---|---|
| General tolerability | Generally well tolerated | Natto itself has centuries of dietary use in Japan; supplement use for up to roughly 3 years appears safe in available reports (WebMD monograph) |
| Bleeding / bruising | Rare but serious — the primary safety concern | Case reports of bleeding events, especially when combined with blood-thinning medications (MSKCC) |
| Gastrointestinal upset | Occasional, mild | Reported anecdotally; not a major theme in the pivotal trials |
| Allergic reaction | Uncommon | As a soy-fermentation product, those with soy allergy should exercise caution |
| Variable vitamin K2 exposure | Product-dependent | Because the enzyme is sourced from natto, some products retain variable vitamin K2 content, which is a pro-coagulant nutrient and a separate consideration from the enzyme itself (MSKCC) |
All interactions
| Drug/substance class | Interaction mechanism | Direction of effect | Severity/guidance |
|---|---|---|---|
| Anticoagulants (warfarin, DOACs such as apixaban/rivaroxaban/dabigatran) | Additive interference with clotting cascade; nattokinase's fibrinolytic action compounds anticoagulant effect | Increased bleeding risk | Avoid without direct medical supervision (MSKCC) |
| Antiplatelets (aspirin, clopidogrel) | Additive antiplatelet/fibrinolytic effect | Increased bleeding risk | Avoid or use only under medical supervision (MSKCC) |
| Other fibrinolytics/thrombolytic drugs | Directly additive fibrinolytic mechanism | Increased bleeding risk | Avoid combination |
| Pre-surgical period | Elevated bleeding risk during and after procedures | Increased surgical bleeding risk | Discontinue before any scheduled surgery or dental procedure (MSKCC) |
| Antihypertensive medications | Nattokinase itself modestly lowers blood pressure via reduced renin activity | Additive blood-pressure lowering | Use with caution; monitor for hypotension (Kim 2008) |
| Vitamin K2 (endogenous to natto-derived products) | Vitamin K2 can antagonize warfarin's mechanism independent of the enzyme's own action | Reduced warfarin effectiveness (opposing direction from the enzyme's bleeding-risk effect) | Check product labeling for K2 content if on warfarin; discuss with a prescriber (MSKCC) |
| Other supplements with antiplatelet activity (e.g., high-dose fish oil, ginkgo, vitamin E) | Potential additive bleeding risk | Increased bleeding risk | Use with caution; no dedicated human interaction trials identified — data gap |
Data gap: There are no dedicated human pharmacokinetic interaction trials for nattokinase with most of these drug classes; guidance above is based on documented case reports and mechanism-based reasoning from independent clinical sources (MSKCC), not controlled interaction studies.
Who should avoid nattokinase
- Anyone currently taking anticoagulants (warfarin, apixaban, rivaroxaban, dabigatran) or antiplatelet drugs (aspirin, clopidogrel) without explicit medical guidance.
- Anyone scheduled for surgery or a dental procedure in the near future — stop use beforehand per a clinician's advice.
- People with bleeding disorders (e.g., hemophilia, von Willebrand disease) or a history of hemorrhagic stroke.
- People with active peptic ulcers or other conditions with elevated bleeding risk.
- Pregnant or breastfeeding people — safety has not been established in this population.
- Anyone with a soy allergy, given nattokinase's origin in fermented soybeans.
- People taking warfarin who are not tracking the vitamin K2 content of their specific nattokinase product.
Dosage and how to take
| Form | Typical studied dose | Duration in trials | Notes |
|---|---|---|---|
| Enteric-coated capsule (standardized to FU) | 2,000 FU/day (~100 mg) | 8 weeks (BP trial); varies across the 6 pooled RCTs | Most common commercial and studied dose (Kim 2008; Li 2023) |
| NSK-SD purified extract | Dosed to match FU activity, generally in line with 2,000 FU/day products | Varies by product/trial | Commonly used purified form in commercial products (RTHM) |
There is no established dose for "dissolving microclots" or treating Long-COVID because no human dosing trial has tested that outcome. Anyone considering nattokinase for blood pressure support — the one claim with human trial backing — should discuss it with a physician first, particularly if already taking blood pressure medication or any blood-thinning drug.
Animal and in-vitro evidence excluded
| Evidence | Type | Reason for exclusion |
|---|---|---|
| Fibrinaloid microclot degradation in blood-sample assays | IN-VITRO (non-human) evidence | Laboratory assay adding nattokinase directly to blood plasma/fibrin plates outside the body; cannot establish that oral nattokinase reaches or dissolves clots in a living person (Liverpool preprint, 2024; bioRxiv, 2024). Not used to support any clinical claim in this article. |
No animal studies were identified as central evidence for nattokinase's primary hyped claims in the source material reviewed for this article; the main non-human evidence gap is the in-vitro microclot work listed above, which is explicitly excluded from all clinical conclusions.
Independent funding and conflict notes
| Source | Funding/affiliation | Independence assessment |
|---|---|---|
| Li 2023, Rev Cardiovasc Med | Academic — Henan University of Chinese Medicine | Independent; no manufacturer funding disclosed |
| Kim 2008, Hypertens Res | Academic — Yonsei University | Independent |
| Liverpool preprint, 2024 | Academic preprint (University of Liverpool) | Academically affiliated, but in-vitro-only and not yet a peer-reviewed clinical trial; excluded from clinical conclusions regardless of independence |
| bioRxiv preprint, 2024 | Academic preprint server | Same limitation as above — in-vitro, not a human clinical trial |
| RTHM supplement guide | Clinic/content publisher discussing a specific branded extract (NSK-SD) | Not an independent research source; treated as a hype/marketing reference point, not evidence |
| Memorial Sloan Kettering Cancer Center herb monograph | Nonprofit academic medical center integrative medicine service | Independent; no manufacturer funding identified for the monograph |
| WebMD ingredient monograph | Health information publisher | Independent secondary reference; not primary research |
The two pivotal human studies supporting the blood-pressure claim (Li 2023 meta-analysis and Kim 2008 RCT) are both academic and carry no disclosed manufacturer funding, making them the most credible evidence in this review. By contrast, much of the microclot/Long-COVID narrative circulating online traces back to content published by sellers of specific purified nattokinase products, and to in-vitro research that has not yet been tested in human clinical trials — both of which warrant caution.
Frequently asked questions
Can nattokinase actually dissolve blood clots or microclots in my body?
There is no human clinical trial evidence that it does. The claim is based on in-vitro laboratory assays showing the enzyme degrades fibrin in blood samples outside the body — a result that cannot be assumed to translate into a living person after oral ingestion (Liverpool preprint, 2024; bioRxiv, 2024). This claim is graded Insufficient.
Does nattokinase help with Long-COVID?
No published human randomized controlled trial has tested this. The Long-COVID "de-clotting" narrative is built on in-vitro microclot assays and patient-community/marketing content, not controlled clinical outcomes (RTHM). This claim is graded Insufficient.
Is nattokinase's blood-pressure benefit real?
Yes, modestly. An independent meta-analysis of 6 RCTs found small but statistically significant reductions in both systolic (−3.45 mmHg) and diastolic (−2.32 mmHg) blood pressure, and an independent standalone RCT found similar results at 2,000 FU/day over 8 weeks (Li 2023; Kim 2008). This is graded Moderate — real, but modest.
Is it safe to take nattokinase with aspirin or warfarin?
Not without medical supervision. Nattokinase's fibrinolytic action is additive with anticoagulants like warfarin and DOACs, and with antiplatelet drugs like aspirin and clopidogrel, raising bleeding risk. Case reports of bleeding events with this combination exist (MSKCC).
Does nattokinase contain vitamin K2?
Because it is extracted from natto, some nattokinase products retain variable amounts of vitamin K2, a nutrient that can reduce the effectiveness of warfarin — the opposite effect from the enzyme's own bleeding-risk profile. Anyone on warfarin should check product labeling and discuss this with a prescriber (MSKCC).
Is nattokinase FDA-approved?
No. It is sold in the United States as a dietary supplement, not an approved drug, and carries no FDA-approved claim to treat, prevent, or dissolve blood clots. Natto itself is a traditional food in Japan, but the concentrated enzyme supplement has not gone through drug approval for any thrombosis-related indication.
Sources and funding notes
- Li 2023, Rev Cardiovasc Med — independent academic meta-analysis of 6 RCTs on nattokinase and cardiovascular risk factors (Henan University of Chinese Medicine).
- Kim 2008, Hypertens Res — independent academic RCT on nattokinase and blood pressure (Yonsei University).
- University of Liverpool preprint, 2024 — in-vitro fibrinaloid microclot degradation assay; excluded from clinical conclusions.
- bioRxiv preprint, 2024 — in-vitro microclot research; excluded from clinical conclusions.
- Memorial Sloan Kettering Cancer Center herb monograph — independent nonprofit reference on nattokinase safety, bleeding risk, and interactions.
- WebMD ingredient monograph — general safety and usage reference.
- RTHM supplement guide — cited as a source of the viral Long-COVID/microclot narrative; treated as marketing-adjacent content, not clinical evidence.
- Rising Trends 2026 — search interest and momentum data for nattokinase.
Last reviewed: July 4, 2026.