HYPE: Nattokinase dissolves blood clots and protects your heart.
But what does the evidence actually show?
Laboratory clot-related activity and some blood-pressure findings are real research signals. Oral nattokinase has not been established as treatment for an existing clot or as a replacement for prescribed anticoagulation.
New unexplained one-sided leg pain or swelling needs urgent help, such as an urgent GP assessment or NHS 111. Chest pain, severe breathing difficulty or collapse needs emergency help: call 999 in the UK. Do not try to dissolve a suspected clot with a supplement. People taking anticoagulants or antiplatelet medicines should not stop or change prescribed treatment because of an online claim. [8]
Why the idea sounds plausible
Nattokinase is an enzyme associated with fermented soybeans called natto. Experimental work examines its effects on fibrin, a protein involved in clots, and related pathways. An enzyme breaking down material under laboratory conditions does not establish safe clot treatment after swallowing a capsule. [3]
Three different claims need separating: changing a coagulation marker, preventing a clinical event and treating an existing clot. Success on the first cannot establish the other two.
What does the evidence show?
No benefit on measured atherosclerosis progression
A double-blind trial randomised 265 adults without clinical cardiovascular disease to nattokinase or placebo. After a median three years, carotid artery-wall thickness and stiffness did not improve compared with placebo. Blood pressure and measured laboratory outcomes also did not significantly differ. This is substantial counter-evidence to broad prevention claims in low-risk healthy adults.
Read the research ↗A modest blood-pressure signal, not proof of clot treatment
Six trials with 546 participants produced pooled systolic and diastolic blood-pressure differences of roughly 3.45 and 2.32 mmHg lower, respectively. Lipid findings were not consistently favourable. These risk-factor outcomes do not show that supplements dissolve established clots or reduce heart attacks and strokes.
Read the research ↗Human clotting markers changed; no clot was treated
Twelve healthy young men received a single 2,000 FU dose or placebo. Over eight hours, selected fibrin-breakdown and coagulation measurements changed, while staying within normal ranges. This is direct human biological evidence, but participants did not have diagnosed clots: the study did not test clot clearance, prevention of thrombosis or emergency treatment. [4]
Read the research ↗A large participant count does not remove confounding
A record-based study of 1,062 supplement users reported improvements in lipids and carotid ultrasound measurements after 12 months. It lacked a randomised placebo comparison; exercise and co-treatments also varied. Before-and-after changes cannot isolate the enzyme’s effect or show fewer heart attacks, strokes or dangerous clots. Plaque measurements concern atherosclerosis, which is different from dissolving an existing thrombus. The reported 10,800 FU daily regimen is a study description, not a recommendation. [5]
Read the research ↗Why findings can differ
Shorter studies and populations with raised blood pressure need not match a longer low-risk trial. Different preparations and follow-up also affect results. The appropriate conclusion is to preserve the possible blood-pressure signal while resisting a universal cardiovascular promise.
A study of an ultrasound marker cannot by itself prove prevention of clinical events. Conversely, its null result does not exclude every possible effect in every population. The headline still needs direct human evidence for the benefit being advertised.
Safety deserves particular attention
Memorial Sloan Kettering warns about potential bleeding risk with anticoagulant, antiplatelet or fibrinolytic medicines, including aspirin, and describes relevant case reports. Case reports cannot estimate how often harm occurs, but absence of notable events in small trials does not establish safety for everyone. [3]
Do not stop warfarin or another prescribed clot-prevention medicine in favour of nattokinase. Food natto also contains vitamin K, which can affect warfarin; food and purified enzyme products are not interchangeable. Seek urgent medical care for symptoms suggesting a clot, stroke or heart attack rather than attempting to dissolve it with a supplement.
Published reports include cerebellar bleeding in a person taking aspirin who also used nattokinase, and fatal abdominal bleeding in an older supplement user. Other illness and circumstances can contribute; these reports do not prove causation or quantify incidence. They do provide reasons to take bleeding and medicine interactions seriously. [6,7]
The catch / limitations
Much of the marketing moves directly from fibrin-related mechanisms to treatment claims. That skips absorption, dose, clinical effectiveness and bleeding risk. A change that affects clotting is not automatically a safe or useful intervention.
The most useful future studies would assess defined products, clinically important events and harms in clearly described populations. More mechanistic activity cannot substitute for those outcomes.
What this means for you
Treat blood-clot claims as medical treatment claims requiring direct clinical evidence. An enzyme demonstration or supplement testimonial cannot answer that question.
Discuss any proposed use with the clinician managing your medicines and clotting risk. The supplement should not replace proven care.
Interesting clot biology; no established oral treatment for blood clots.
Research & Sources
1. Hodis et al.: Nattokinase atherothrombotic prevention trial (2021)
Original source ↗2. Li et al.: Nattokinase Supplementation and Cardiovascular Risk Factors: A Systematic Review and Meta-Analysis of Randomized Controlled Trials (2023)
Original source ↗3. Memorial Sloan Kettering: Nattokinase, clinical summary and safety
Original source ↗4. Kurosawa et al. (2015): single-dose crossover biomarker trial
Original source ↗5. Chen et al. (2022): retrospective study of 1,062 participants
Original source ↗6. Chang et al. (2008): cerebellar haemorrhage with aspirin; case report
Original source ↗7. Ramachandran et al. (2021): nattokinase-associated haemoperitoneum; case report
Original source ↗8. NHS: pulmonary embolism symptoms and urgent assessment
Original source ↗Correction, October 2026: Corrected the publication year and formal citation of the nattokinase review; the WEAK verdict is unchanged.
Evidence reviewed: October 2026
Evidence vs Hype explains scientific research for educational purposes and does not provide individual medical diagnosis or treatment. Featured artwork illustrates the claim being investigated; conceptual insets do not demonstrate a proven biological effect.