Who Should Not Use Nattokinase? A Guide to Contraindications and Risks

October 8, 2025 •

3 min read

Nattokinase, an enzyme derived from fermented soybeans, is widely recognized for its fibrin-dissolving properties, which may promote healthy blood flow. However, due to its potent effect on blood coagulation, understanding who should not use nattokinase is critical for preventing serious bleeding risks and other complications.

Quick Summary

Individuals taking blood-thinning or antiplatelet drugs, those with bleeding disorders, or people scheduled for surgery should avoid nattokinase supplements. Consultation with a healthcare provider is essential before starting nattokinase to prevent excessive bleeding or other adverse effects.

Key Points

Avoid with blood thinners: Do not use nattokinase if you are on anticoagulant medications like warfarin or antiplatelet drugs like aspirin, as this can dramatically increase bleeding risk.
Contraindicated for bleeding disorders: Individuals with bleeding disorders such as hemophilia should not use nattokinase due to the risk of uncontrolled bleeding.
Discontinue before surgery: Stop taking nattokinase at least two weeks prior to any surgery or dental procedure to minimize the risk of excessive bleeding.
Not for pregnancy or breastfeeding: Safety data is lacking for these groups; therefore, nattokinase should be avoided by pregnant or breastfeeding women.
Allergy risk: Since nattokinase is derived from fermented soy, people with soy or natto allergies should not use it to prevent allergic reactions.
Potential hypotension risk: Those with low blood pressure or on blood pressure-lowering medication should use caution, as nattokinase can further lower blood pressure.

What is Nattokinase and How Does It Work?

Nattokinase is a proteolytic enzyme isolated from natto, a traditional Japanese fermented soybean food. It is known for its fibrinolytic activity, meaning it can help break down fibrin, a protein involved in blood clot formation. This property has led to its promotion as a dietary supplement for cardiovascular health, with claims that it can help reduce blood pressure and prevent the formation of blood clots. However, this same mechanism of action is why it carries significant risks for certain individuals and requires medical supervision.

Key Groups Who Should Avoid Nattokinase

Individuals on Blood-Thinning Medications

The most significant contraindication for nattokinase is its combination with anticoagulant and antiplatelet drugs. Nattokinase's natural blood-thinning effect can dangerously amplify the effects of these prescription medications, leading to a greatly increased risk of excessive bleeding and bruising. In extreme cases, this interaction can cause life-threatening internal or cerebral hemorrhage. A documented case involved an elderly woman who died from hemoperitoneum after taking nattokinase while not on other blood thinners, highlighting the supplement's inherent risks.

Common medications that should not be combined with nattokinase include:

Anticoagulants: Warfarin (Coumadin), heparin, and newer oral anticoagulants like apixaban (Eliquis) and rivaroxaban (Xarelto).
Antiplatelets: Aspirin, clopidogrel (Plavix), and prasugrel (Effient).
NSAIDs: Nonsteroidal anti-inflammatory drugs such as ibuprofen and naproxen, which also have blood-thinning properties.

Patients with Bleeding Disorders

People with pre-existing bleeding disorders, such as hemophilia, should never use nattokinase. The enzyme's effect on blood clotting can exacerbate their condition and lead to uncontrolled bleeding episodes. A case report also noted cerebellar hemorrhage in a patient with cerebral microbleeds who combined nattokinase with aspirin.

Individuals Scheduled for Surgery

Because of its powerful fibrinolytic properties, nattokinase must be discontinued before any surgical or dental procedure. Most healthcare professionals recommend stopping the supplement at least two weeks prior to surgery to minimize the risk of excessive intraoperative and postoperative bleeding complications.

Pregnant or Breastfeeding Women and Children

There is a severe lack of research and safety data concerning the use of nattokinase during pregnancy or breastfeeding. For this reason, doctors strongly advise against its use in these populations to avoid potential harm to the mother or child. Similarly, due to insufficient safety information, nattokinase is not recommended for children.

People with Soy Allergies

Nattokinase is derived from fermented soybeans. Therefore, individuals with an allergy to soy or natto should avoid nattokinase supplements to prevent an allergic reaction. Some severe allergic reactions, including anaphylaxis, have been reported in sensitive individuals.

Potential Drug Interactions with Nattokinase

Nattokinase is a powerful enzyme that can interact with more than just blood thinners. Anyone considering taking nattokinase must discuss all other medications and supplements with their doctor to prevent dangerous interactions.

Interaction Risks for Nattokinase Users


User Group	Potential Nattokinase Interactions & Risks	Professional Recommendation
On Anticoagulants (e.g., Warfarin)	Severely increases bleeding risk, potentially causing life-threatening hemorrhage.	Absolutely avoid. Never substitute nattokinase for a prescribed anticoagulant.
On Antiplatelets (e.g., Aspirin)	Increases risk of excessive bleeding and bruising.	Discuss with a healthcare provider; strict supervision and potential dosage adjustment needed.
On Antihypertensives	May cause blood pressure to drop too low, especially when taken with ACE inhibitors or calcium channel blockers.	Monitor blood pressure closely with a doctor; dosage may need adjustment.
With Bleeding Disorders	Can worsen the condition, leading to uncontrolled bleeding episodes.	Absolutely avoid due to high risk of bleeding complications.
Pre- or Post-Surgery	Increases risk of bleeding during or after the procedure.	Stop taking at least two weeks before any scheduled surgery.

Conclusion

While nattokinase is promoted for various cardiovascular benefits, its potent blood-thinning properties make it dangerous for certain individuals. Anyone taking anticoagulant or antiplatelet medications, those with bleeding disorders, and patients facing upcoming surgery should strictly avoid nattokinase supplements. It is imperative to consult a qualified healthcare provider before starting any new supplement, including nattokinase, to ensure it is safe for your specific health situation and to prevent potentially severe complications. For more information, the Memorial Sloan Kettering Cancer Center provides a detailed overview of nattokinase and its potential risks.

Frequently Asked Questions

No, you should not take nattokinase if you are on a blood thinner like warfarin. Nattokinase's natural blood-thinning effect can dangerously amplify the effects of these medications, significantly increasing the risk of serious bleeding.

You should stop taking nattokinase at least two weeks before any scheduled surgery or major dental work. This is to prevent excessive bleeding complications during and after the procedure.

No, it is not recommended to use nattokinase while pregnant or breastfeeding. There is insufficient clinical data to confirm its safety for these populations, so it should be avoided.

Yes, nattokinase can cause an allergic reaction, especially in individuals with a known allergy to soybeans or natto. In rare cases, severe allergic responses, including anaphylaxis, have been reported.

Nattokinase can lower blood pressure, which may be problematic for people already dealing with low blood pressure or taking blood pressure-lowering medications. This combination could cause blood pressure to drop to an unsafe level, leading to dizziness or fainting.

Yes, nattokinase can interact with other medications. It can intensify the effects of antihypertensive drugs and some NSAIDs, increasing the risk of excessively low blood pressure or heightened bleeding.

Individuals with a history of stroke, particularly ischemic stroke, or with cerebral vascular lesions should use nattokinase with extreme caution and only under medical supervision. There is a theoretical risk that its clot-dissolving properties could cause an existing clot to dislodge, leading to further complications.