Is nattokinase hard on your liver?

Nattokinase does not appear on any hepatologist's list of liver-damaging supplements, and after nearly four decades of human use, that absence is the most useful evidence there is.

Herbal and dietary supplements now account for 20% of drug-induced liver injury cases in the United States, and the repeatedly named culprits are anabolic steroids, green tea extract, and multi-ingredient blends. Nattokinase is not among them. Its 90-day toxicology threshold sits at 1,000 mg/kg per day — the highest dose anyone has tested.

Table of Contents

• 1. The Short Answer
• 2. What Safety Testing Actually Found
• 3. Liver Function in Human Nattokinase Studies
• 4. The One Published Case Report
• 5. The Real Risk Is What's Blended In Beside It
• 6. Who Should Be Cautious, and What to Watch
• 7. BioAbsorb Nattokinase Enzyme — Why a Single-Ingredient Formula Matters Here
• Frequently Asked Questions
• Conclusion
• Research References

1. The Short Answer

No published toxicology study, randomised trial, or clinical registry has established nattokinase as hepatotoxic. The enzyme was first identified in 1987, has been sold as a supplement worldwide for more than two decades, and across the full toxicology battery it was non-mutagenic and non-clastogenic in vitro with no adverse effects in either the 28-day or 90-day rat studies.

That is not the same as saying nothing has ever gone wrong. There is one published case of possible liver injury involving a nattokinase-containing product, covered in Section 4, and it deserves an honest reading rather than a dismissal. But the pattern across roughly 1,400 people in the three largest nattokinase safety datasets points in one direction, and it is not toward the liver.

• Rat 90-day NOAEL: 1,000 mg/kg per day, the highest dose tested — no harm ceiling identified
• Longest monitored human exposure: 265 participants, 3 years, laboratory measures every 6 months
• Published cases of liver injury attributed to nattokinase alone: none identified in the literature reviewed here

2. What Safety Testing Actually Found

The most rigorous safety assessment of nattokinase is a set of GLP-compliant studies published in Food and Chemical Toxicology. Rats given the enzyme by gavage for 90 days showed no adverse effects at 1,000 mg/kg per day, and the 28-day study reached 167 mg/kg per day with the same result. A separate acute toxicity and genotoxicity evaluation dosed mice at the maximum feasible concentration without producing mortality or any toxicological sign, placing the maximum tolerated daily dose at roughly 1,000 times the recommended human intake.

The detail that matters most is the phrase "highest dose tested." A no-observed-adverse-effect level is normally bracketed by a dose where something does happen. Here, researchers stopped at 1,000 mg/kg per day without finding a threshold. On a simple body-weight basis that figure corresponds to roughly 700 times the 100 mg in a single daily capsule for a 70 kg adult — a crude comparison rather than a formal human-equivalent dose, but a wide margin by any reading.

Human data from the same assessment is more modest in scale and more directly relevant. Healthy volunteers took 10 mg/kg per day for 4 weeks with clinical chemistry monitored and tolerated it well, which for a 70 kg adult works out to about 7 times a standard 100 mg daily serving. A 2025 review in Nutrients summarising long-term use concluded that the incidence of adverse reactions is very low, limited mainly to minor gastrointestinal discomfort such as bloating or belching that resolves with a change in dose or timing.

3. Liver Function in Human Nattokinase Studies

The cleanest evidence comes from the longest trial, because it tested nattokinase on its own. In a double-blinded randomised study, 265 participants of median age 65.3 took 2,000 FU daily for a median of 3 years, with clinical parameters and laboratory measures — including coagulation and fibrinolysis factors — repeated at least every 6 months. The trial found no benefit for subclinical atherosclerosis, a genuinely negative efficacy result worth knowing, and it also reported no significant effect on blood pressure or on any laboratory determination. Three years of monitored exposure with no laboratory signal is the single most useful safety datapoint available.

The largest dataset is bigger but weaker. It followed 1,062 participants taking 10,800 FU per day for 12 months — about 5 times the 2,000 FU dose on most supplement labels — with fasting blood work including liver and kidney function before and after, and recorded no noticeable adverse effects. Three caveats belong with that finding: the study was retrospective rather than randomised, 5 of its authors were employed by the nattokinase manufacturer, and a corrigendum was subsequently published.

A third trial is often quoted in this context and needs a careful reading. A 4-month randomised, double-blind, placebo-controlled study in 113 people with dyslipidemia reported no significant differences in coagulation, liver function, renal function, or other safety indicators over 120 days. But the product tested was a nattokinase and red yeast rice combination, not nattokinase alone — so it does not isolate the enzyme. What it does tell you is more interesting, and it belongs in Section 5: even the combination did not move liver function.

Real-world data adds a different angle. A pharmacovigilance study followed 153 patients admitted to vascular surgery who were naive to anticoagulant and antiplatelet therapy and then given nattokinase at 100 mg per day, in two of three groups alongside protocol anticoagulation, and recorded no adverse drug reactions or drug interactions. And a 2023 systematic review pooling 6 randomised trials in 546 participants found the overall methodological quality of the evidence base to be high.

4. The One Published Case Report

In 2025, clinicians presented a case of cholestatic or mixed-pattern liver injury in a 55-year-old man in which symptoms appeared 4 days after he began a nattokinase and serrapeptase product while already taking semaglutide. The authors judged drug-induced liver injury likely after excluding other causes, and noted that both enzymes are unregulated and lack hepatotoxicity data.

Read carefully, the report is a caution rather than a verdict. Three agents were in play, the patient had a documented history of moderate alcohol use, the authors explicitly could not rule out semaglutide given the rebound in liver enzymes after discontinuation, and a 4-day onset is unusually fast for idiosyncratic injury. Against nearly four decades of use and roughly 1,440 participants across the monitored trials above, one confounded case is a reason to pay attention to your own labs — not evidence that the enzyme damages livers.

It also illustrates why AASLD practice guidance emphasises that diagnosing supplement-related liver injury requires excluding more common competing causes first. The same guidance notes that there are more than 100,000 over-the-counter supplement products available in the US and that the average adult American receives more than six prescription medications a year. Attributing a change in liver enzymes to any single ingredient is harder than it looks.

5. The Real Risk Is What's Blended In Beside It

Here is the finding that reframes the question. When researchers catalogued the supplements behind US liver injury cases, the named agents were anabolic steroids, green tea extract, and multi-ingredient nutritional supplements — that third category being the problem for anyone shopping for a fibrinolytic enzyme, because nattokinase is very often sold blended with other actives. In the decade-long network analysis, the products that led most often to death or transplantation were the non-bodybuilding, multi-ingredient ones, at 13% versus 3% for conventional medications.

The clearest example is red yeast rice, the most common nattokinase companion ingredient in cardiovascular formulas. The 113-person combination trial from Section 3 also noted that citrinin, a toxin found naturally in red yeast rice, has been associated with hepatotoxicity and nephrotoxicity. Red yeast rice also supplies monacolin K, which is chemically identical to a prescription statin. If a combination product moves your liver enzymes, the enzyme in the name is rarely the ingredient that did it.

This is why the composition on the label matters more than the ingredient in the headline:

• Single-ingredient nattokinase: one variable to evaluate, and the one with the strongest safety dossier
• Nattokinase + red yeast rice: adds citrinin and statin-equivalent monacolin K to the picture
• Multi-enzyme blends: the 2025 case report involved two enzymes plus a prescription drug
• Untested products: without batch testing, contaminant load is unknown regardless of the active

The BioAbsorb Nattokinase Enzyme formula is deliberately single-ingredient at 100 mg (2000 FU) per capsule, with no red yeast rice and no Vitamin K2 — which removes the co-ingredients most likely to complicate a liver question.

6. Who Should Be Cautious, and What to Watch

The legitimate liver-related concern with nattokinase is not hepatotoxicity — it is clotting. The liver manufactures most clotting factors, so people with meaningful liver disease often already have altered haemostasis. Adding a fibrinolytic enzyme to that picture is a decision for a physician, not a label. The same logic applies to anyone on anticoagulants, which is covered in more depth in our guide to nattokinase as a natural blood thinner.

Anyone with existing liver disease, hepatitis, or unexplained enzyme elevations should get clearance before starting, as should anyone taking an anticoagulant or antiplatelet medication. If liver enzymes do rise while you are taking any supplement, AASLD guidance is to stop the product and investigate systematically rather than assume a cause — a rise of more than 3 times the upper limit of normal warrants prompt medical review.

Worth noting for balance: in animal models nattokinase has looked protective rather than harmful, with improved liver function tests in rats exposed to bisphenol A or gamma irradiation. Animal findings do not transfer directly to people, and no clinical trial has tested nattokinase as a liver treatment, so this belongs in the "reassuring, not actionable" column. For the broader tolerability picture, see our breakdown of nattokinase side effects and when to stop.

7. BioAbsorb Nattokinase Enzyme — Why a Single-Ingredient Formula Matters Here

If the category risk comes from co-ingredients and unverified contents, then formulation discipline is the practical answer. BioAbsorb Nattokinase Enzyme delivers 100 mg of nattokinase per capsule at 2000 FU of measured activity, taken once daily, with nothing else active in the capsule — no red yeast rice, no Vitamin K2, no proprietary enzyme blend.

That 2000 FU serving sits at the dose used in the 3-year monitored trial discussed above, well below the 10,800 FU studied for 12 months. It is a deliberately conservative position rather than a race to the highest number on the shelf.

Every batch is third-party tested in a Canadian GMP-certified facility for nattokinase activity, plus heavy metals, gluten, and microbial contaminants. Contaminant testing is directly relevant to a liver question, because in documented supplement liver injury cases the culprit is frequently an undeclared or contaminating compound rather than the labelled active. The DRcaps delayed-release capsule protects the enzyme from stomach acid without the phthalates and plasticizers used in conventional enteric coatings, and the formula is non-GMO, 100% vegetarian, and free of gluten, nuts, eggs, dairy, fish, and shellfish. Practical dosing details are in our nattokinase dosage guide.

Frequently Asked Questions

Do I need a liver panel before starting nattokinase?

Not as a rule, if you are healthy and taking a single-ingredient product at 2000 FU. A baseline panel is genuinely useful if you have any history of liver disease, drink regularly, or take two or more medications — mostly because it gives you a comparison point later. In the 3-year randomised trial, no laboratory measure differed significantly from placebo.

Can I take nattokinase if I have fatty liver disease?

Ask your physician first, and the reason is clotting rather than enzyme damage. Advanced liver disease alters the production of clotting factors, so a fibrinolytic enzyme changes a balance that is already disturbed. No trial has specifically tested nattokinase in people with fatty liver disease, which is itself a reason for caution rather than reassurance.

What should I do if my liver enzymes rise while taking it?

Stop the supplement and contact your doctor, particularly if the rise exceeds 3 times the upper limit of normal. AASLD practice guidance is to exclude more common causes systematically instead of assuming the supplement is responsible, and bring the actual bottle so every ingredient can be reviewed.

Are nattokinase and red yeast rice combination products riskier for the liver?

They warrant more caution, yes. Red yeast rice contributes monacolin K, a statin-equivalent compound, and can carry citrinin, a natural toxin associated with hepatotoxicity. The 120-day trial of that combination did not find liver function changes, but a single-ingredient nattokinase still removes one significant variable from the equation.

Is eating natto easier on the liver than taking a supplement?

Neither has been shown to burden the liver, so there is no clear advantage either way. The practical difference is dose consistency: a supplement standardised to 2000 FU delivers a known quantity, while natto's enzyme content varies by batch and fermentation. Our complete guide to nattokinase compares food and supplement sources in detail.

Conclusion

Across nearly four decades of use, a 90-day toxicology study that never found a harmful dose, and roughly 1,440 monitored trial participants including 265 followed for 3 years, nattokinase has not emerged as a liver risk — while the co-ingredients it is commonly blended with have. If you want the enzyme without the complications, a single-ingredient, batch-tested formula answers the question before it arises: see BioAbsorb Nattokinase Enzyme, 100 mg / 2000 FU.

Research References

1. Toxicological assessment of nattokinase derived from Bacillus subtilis var. natto. Food and Chemical Toxicology, Vol. 88 (2016), pp. 87–99. GLP-compliant battery finding nattokinase non-mutagenic and non-clastogenic, with a 90-day oral subchronic NOAEL of 1,000 mg/kg per day in rats — the highest dose tested — and good tolerance at 10 mg/kg per day in a 4-week human study.
2. Acute toxicity and genotoxicity evaluations of nattokinase, a promising agent for cardiovascular diseases prevention. Regulatory Toxicology and Pharmacology, Vol. 103 (2019), pp. 205–209. Acute oral dosing in mice at maximum feasible concentration produced no mortality or toxicological signs, establishing a maximum tolerated daily dose approximately 1,000 times the recommended human intake.
3. Nattokinase atherothrombotic prevention study: A randomized controlled trial. Clinical Hemorheology and Microcirculation, Vol. 78, Issue 4 (2021), pp. 339–353. Double-blinded trial of 265 participants at 2,000 FU daily for a median of 3 years with laboratory monitoring at least every 6 months; null effect on subclinical atherosclerosis progression and no significant effect on blood pressure or any laboratory determination.
4. Effective management of atherosclerosis progress and hyperlipidemia with nattokinase: A clinical study with 1,062 participants. Frontiers in Cardiovascular Medicine, Vol. 9 (2022), article 964977. Retrospective analysis of 12 months at 10,800 FU daily with liver and kidney function tested; no noticeable adverse effects recorded. Five authors were employed by the manufacturer. A corrigendum was published in December 2022 (doi 10.3389/fcvm.2022.1076420).
5. The Effect of Nattokinase-Monascus Supplements on Dyslipidemia: A Four-Month Randomized, Double-Blind, Placebo-Controlled Clinical Trial. Nutrients, Vol. 15, Issue 19 (2023), article 4239. Trial of a nattokinase and red yeast rice combination product in 113 subjects, finding no significant differences in liver function, renal function, or coagulation over 120 days, and documenting citrinin in red yeast rice as a hepatotoxicity concern.
6. Data Recorded in Real Life Support the Safety of Nattokinase in Patients with Vascular Diseases. Nutrients, Vol. 13, Issue 6 (2021), article 2031. Pharmacovigilance evaluation of nattokinase at 100 mg daily in 153 vascular surgery patients who were naive to anticoagulant and antiplatelet therapy at enrolment; no adverse drug reactions or drug interactions recorded.
7. Nattokinase Supplementation and Cardiovascular Risk Factors: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Reviews in Cardiovascular Medicine, Vol. 24, Issue 8 (2023). Pooled analysis of 6 randomised controlled trials with 546 participants; overall methodological quality of included studies assessed as high.
8. Research Progress of Nattokinase in Reducing Blood Lipid. Nutrients, Vol. 17, Issue 11 (2025). Review concluding that long-term nattokinase use carries a very low incidence of adverse reactions, mainly minor gastrointestinal discomfort, and noting that its absorption pathway is not fully elucidated.
9. Liver injury from herbals and dietary supplements in the U.S. Drug-Induced Liver Injury Network. Hepatology, Vol. 60, Issue 4 (2014), pp. 1399–1408. Prospective network study in which supplement-attributed liver injury rose from 7% to 20% of cases, with non-bodybuilding products producing worse outcomes — death or transplantation in 13% versus 3% for conventional medications.
10. Liver injury from herbal and dietary supplements. Hepatology, Vol. 65, Issue 1 (2017), pp. 363–373. Establishes that supplements account for 20% of US hepatotoxicity cases and identifies anabolic steroids, green tea extract, and multi-ingredient supplements as the principal implicated agents.
11. Nattokinase attenuates bisphenol A or gamma irradiation-mediated hepatic and neural toxicity by activation of Nrf2 and suppression of inflammatory mediators in rats. Environmental Science and Pollution Research International, Vol. 29, Issue 49 (2022), pp. 75086–75100. Animal study reporting improved liver function tests in rats following chemically or radiation-induced liver damage. A correction to two figures was published in 2026; the reported data are unaffected.
12. AASLD practice guidance on drug, herbal, and dietary supplement-induced liver injury. American Association for the Study of Liver Diseases, published in Hepatology, Vol. 77, Issue 3 (2023), pp. 1036–1065. Clinical guidance on diagnosing and managing supplement-related liver injury, including the requirement to exclude competing causes, and the source of the market-size and prescription-volume figures cited in Section 4.
13. Weight Loss or Liver Loss? Cholestatic Injury (abstract S5864). American Journal of Gastroenterology, Vol. 120, Issue 10S2 (October 2025), p. S7. Case report of likely drug-induced cholestatic liver injury in a 55-year-old man with a moderate alcohol history, beginning 4 days after starting a nattokinase/serrapeptase product alongside semaglutide, with causality unestablished.

About the Author

David Kimbell is a health writer, digital entrepreneur and former aerospace engineer, based in Ottawa, Canada. He loves translating complex science into clear, actionable guidance for consumers seeking evidence-based solutions.

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Important Disclaimers

Medical Disclaimer: This article provides educational information only and is not intended as medical advice. Always consult with a qualified healthcare provider before starting any new supplement, especially if you have existing health conditions, take medications, or are pregnant or nursing.

FDA/Health Canada Statement: These statements have not been evaluated by the Food and Drug Administration or Health Canada. This product is not intended to diagnose, treat, cure, or prevent any disease.