Table of Contents
Key Takeaways:
Nattokinase is generally well-tolerated, but some people should be mindful.
Because nattokinase has fibrinolytic activity, people taking anticoagulants, antiplatelet medications, or regular aspirin should consult their healthcare provider before using it.
Talk to your healthcare provider before starting nattokinase if you take medication, have a bleeding disorder, are preparing for surgery, are pregnant or breastfeeding, or have an existing cardiovascular condition.
Nattokinase is a fibrinolytic enzyme originally identified in natto, a traditional Japanese food made from fermented soybeans. It has become a popular dietary supplement for people interested in supporting their cardiovascular and circulatory health, and the research behind it is more substantive than you might expect.
That said, "natural" doesn't necessarily mean risk-free, and nattokinase is a good example of why that distinction matters. Nattokinase has real biological activity, which is what makes it interesting, but that’s also exactly why some people need to approach it a bit more carefully. Potential side effects, medication interactions, allergies, and individual health conditions should all be considered before adding it to your routine.
What Are the Potential Side Effects of Nattokinase?
It’s important to know that the research on nattokinase is still developing, and its complete long-term safety profile hasn't yet been fully established. That said, available human studies do suggest that it's generally well tolerated, but here's what you should be aware of.
Dizziness or Lightheadedness
Nattokinase has demonstrated modest blood pressure-lowering effects in clinical research. In a randomized, double-blind, placebo-controlled trial, researchers gave 86 adults with untreated prehypertension or stage 1 hypertension either 2,000 fibrinolytic units (FU) of nattokinase or a placebo for eight weeks. Among the 73 participants who completed the study, the nattokinase group experienced modest reductions in systolic and diastolic blood pressure compared with placebo.
These findings are promising, but nattokinase’s possible influence on blood pressure also means that people who already have low blood pressure or take antihypertensive medication should discuss supplementation with their healthcare provider before starting it. In those people, the added blood-pressure effect may show up as dizziness or lightheadedness.
Increased Bleeding or Bruising
The most important potential nattokinase side effect involves bleeding due to blood-thinning effects. Because nattokinase has fibrinolytic activity, combining it with medications that affect coagulation or platelet function may increase bleeding risk.
A published case report described a patient taking aspirin for secondary stroke prevention who developed an acute cerebellar hemorrhage after adding nattokinase. The patient also had cerebral microbleeds that increased her underlying bleeding risk. A single case report certainly can't establish causation, but it does point to the fact that combining supplements that influence clotting with antithrombotic medications requires medical supervision and guidance.
Talk to your doctor before taking nattokinase if you use aspirin, warfarin, another anticoagulant, an antiplatelet medication, or any other medication that affects bleeding or clotting.
One more thing: You should never use nattokinase to self-treat a suspected blood clot. Sudden shortness of breath, chest pain, coughing up blood, one-sided leg swelling or pain, facial drooping, difficulty speaking, or sudden weakness can indicate a medical emergency. Call 911 or seek emergency medical attention immediately.
Allergic Reactions and Soy
Traditional nattokinase is produced from natto, which is made from fermented soybeans. As a result, anyone with a soy allergy should pay particular attention to the source and manufacturing of a nattokinase supplement before using it.
Potential signs of an allergic reaction can include:
Hives, itching, or a skin rash
Swelling of the lips, face, tongue, or throat
Stomach cramps, nausea, or vomiting
Wheezing or difficulty breathing
Dizziness or fainting
Severe allergic reactions can be life-threatening. Difficulty breathing, significant facial or throat swelling, fainting, or other symptoms of anaphylaxis require immediate emergency medical attention.
Our Toku Flow uses soy-free nattokinase, making it a safe option for those with soy allergies. People with significant food allergies should still discuss new dietary supplements with their healthcare provider.
Does Nattokinase Have Liver or Kidney Risks?
Unlike statins’ potential effects on the liver, current research shows no evidence that nattokinase does the same. In fact, one animal study showed that it may have liver-protective effects.
Researchers tested whether high doses of nattokinase could protect the liver from damage caused by a harmful chemical. They found that nattokinase lowered liver enzymes that signal liver problems, reduced inflammation, and boosted defenses to help prevent liver cell death.
This sets the stage for more studies about reducing liver inflammation in toxin-related liver conditions like alcohol use disorders. The evidence so far indicates nattokinase is safe, even beneficial, for the liver.
For kidney health as well, the current evidence doesn't point to meaningful kidney harm.
A published toxicological evaluation of nattokinase included both a 90-day animal study and human safety monitoring. Standard kidney function markers, including blood creatinine, urea, and uric acid, stayed within normal ranges throughout. A small number of participants showed minor, isolated changes on urinalysis, such as trace protein or occult blood. However, bloodwork showed no corresponding evidence of kidney dysfunction, so researchers considered these findings incidental rather than indicative of kidney injury.
Does Nattokinase Interact With Medications?
The short answer is that yes, nattokinase does have the potential to interact with certain medications.
Particular caution may be warranted with anticoagulant and antiplatelet medications, due to nattokinase's fibrinolytic activity. Combining multiple substances that affect normal coagulation could potentially increase the chance of bruising or bleeding.
There may also be reasons for caution with blood pressure medications. An eight-week randomized controlled trial found modest blood-pressure reductions among people taking nattokinase, although more research is needed to understand this effect.
Never discontinue or reduce a prescription medication in order to take nattokinase. Nattokinase has not been established as a replacement for anticoagulants, antiplatelet medications, statins, antihypertensive drugs, or other cardiovascular treatments.
If you're taking prescription medication, show your doctor or pharmacist the supplement label before beginning nattokinase. This makes it easier to evaluate the complete ingredient list and potential interactions.
The Bottom Line on Nattokinase Side Effects
Nattokinase is an increasingly studied dietary supplement with fibrinolytic activity and potential applications for cardiovascular wellness. Human research has produced interesting findings, including nattokinase having modest effects on blood pressure in some trials, while other areas still require stronger randomized clinical evidence.
For most people, the biggest considerations around nattokinase are potential interactions with medications, bleeding risk, blood pressure effects, allergies, and choosing an appropriate supplement. If you take cardiovascular medication, have a bleeding disorder, are preparing for surgery, or have an existing health condition, speak with your healthcare provider before taking nattokinase.
FAQs
Who should not take nattokinase?
People taking anticoagulants, antiplatelet medications, or regular aspirin should speak with their doctor before taking nattokinase because of potential bleeding concerns. People with bleeding disorders or upcoming surgical procedures should also seek medical guidance. Pregnant or breastfeeding individuals should consult a healthcare professional because safety research in these populations is limited.
What are the most important nattokinase side effects?
Potential concerns include bleeding or bruising and possible dizziness or lightheadedness related to changes in blood pressure. Allergic reactions are another consideration, depending on the ingredients and source of the supplement.
Can nattokinase replace blood thinners or statins?
No. Nattokinase has not been established as a replacement for anticoagulants, statins, blood-pressure medication, or other prescribed cardiovascular treatments. Never stop or modify prescribed medication without consulting the clinician who manages your care.
*The information provided in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives. This content has not been evaluated by the Food and Drug Administration and is not intended to diagnose, treat, cure or prevent any disease.
Sources:
Effects of nattokinase on blood pressure: a randomized, controlled trial | PubMed
Know the Risks, Signs & Symptoms of Blood Clots | CDC
Toxicological assessment of nattokinase derived from Bacillus subtilis var. natto | PubMed
