Nattokinase is an enzyme extracted from a traditional Japanese food called natto, which is made from fermented soybeans [1.5.2]. It has gained attention for its potential cardiovascular benefits, particularly its ability to break down fibrin, a protein involved in blood clotting [1.5.6]. While many turn to nattokinase as a natural alternative for supporting circulation, it's essential to be fully aware of its potential risks and side effects before use.
The Primary Concern: Bleeding Risk
The most significant negative side effect associated with nattokinase is an increased risk of bleeding [1.2.4]. Its fibrinolytic (clot-dissolving) properties mean it can thin the blood [1.3.1]. This effect can lead to:
- Excessive bruising [1.3.1].
- Prolonged bleeding from injuries [1.2.4].
- In rare cases, serious internal bleeding. There is a case report of a cerebellar hemorrhage in a patient who used both nattokinase and aspirin [1.3.3]. Another case reported internal bleeding leading to death in an elderly woman taking over-the-counter nattokinase who was not on other blood thinners [1.2.1].
Because it can prolong clotting times, individuals with any existing bleeding disorders, such as hemophilia, should avoid nattokinase [1.4.4, 1.6.1]. Furthermore, to minimize the risk of excessive bleeding during and after surgical procedures, it is recommended to stop taking nattokinase at least two weeks before a scheduled surgery [1.5.2].
Theoretical Risk of Embolism
Another concern, though theoretical, is the risk of dislodging an existing blood clot [1.2.1]. The potent clot-dissolving action could break a piece of a clot free, which could then travel to another part of the body, such as the lungs or brain, causing an embolism or stroke [1.2.7]. For this reason, individuals with a history of deep vein thrombosis (DVT) are advised to avoid nattokinase [1.2.5].
Significant Drug Interactions
Understanding how nattokinase interacts with other medications is crucial for safety. The most critical interactions are with drugs that also affect blood clotting and blood pressure.
Anticoagulant and Antiplatelet Drugs
Combining nattokinase with blood-thinning medications can dangerously increase the risk of bleeding [1.3.7]. Individuals taking the following medications should not use nattokinase without consulting a healthcare provider:
- Prescription Anticoagulants: This includes drugs like warfarin (Coumadin) and heparin [1.3.6]. A case report noted that a patient who substituted warfarin with nattokinase developed a thrombus on a mechanical heart valve, requiring a repeat valve replacement [1.3.3].
- Antiplatelet Drugs: This includes daily aspirin and clopidogrel (Plavix) [1.3.1, 1.3.2]. Taking nattokinase with aspirin may increase the risk of intracerebral hemorrhage [1.4.2].
- Over-the-Counter Pain Relievers: Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen (Advil, Motrin) and naproxen can also have a mild blood-thinning effect, which could be amplified by nattokinase [1.3.1].
Blood Pressure Medications
Studies suggest that nattokinase may lower blood pressure [1.7.5]. When taken with antihypertensive (high blood pressure) medications, this effect can be additive, potentially causing blood pressure to drop too low (hypotension) [1.7.1]. Symptoms of hypotension include dizziness, lightheadedness, and fainting [1.7.2, 1.6.1]. Close monitoring of blood pressure is essential if combining nattokinase with drugs like ACE inhibitors or calcium channel blockers [1.3.6].
Who Should Avoid Nattokinase?
Based on the potential side effects and interactions, several groups of people should exercise caution or completely avoid using nattokinase supplements:
- People with Bleeding Disorders: Individuals with conditions like hemophilia or other coagulation disorders should not take nattokinase [1.4.3].
- Individuals on Blood-Thinning Medication: Anyone taking anticoagulants or antiplatelet drugs should avoid nattokinase unless explicitly approved and monitored by a doctor [1.6.2].
- People Scheduled for Surgery: Discontinue use at least two weeks prior to any surgical or dental procedure to reduce the risk of excessive bleeding [1.4.6].
- Pregnant and Breastfeeding Women: Due to a lack of research on its safety in these populations, nattokinase is not recommended during pregnancy or while breastfeeding [1.4.3].
- Individuals with Soy Allergies: Since nattokinase is derived from fermented soybeans, those with a soy allergy could experience an allergic reaction [1.6.2]. Symptoms can range from rash and itching to severe anaphylaxis [1.8.1, 1.4.2].
- Those with a History of Stroke or Peptic Ulcers: Use should be avoided in individuals who have had an ischemic stroke or have peptic ulcers due to bleeding risks [1.6.3].
Comparison: Nattokinase vs. Daily Aspirin
Many consider nattokinase as a natural alternative to a daily low-dose aspirin for cardiovascular protection. Here is a comparison of the two:
| Feature | Nattokinase | Low-Dose Aspirin |
|---|---|---|
| Mechanism | A fibrinolytic enzyme that directly breaks down fibrin, a key component of blood clots [1.5.6]. It may also lower blood pressure [1.7.5]. | An antiplatelet drug that inhibits cyclooxygenase (COX) enzymes, reducing the production of thromboxane A2, which prevents platelets from aggregating to form clots [1.4.2]. |
| Primary Use | Dietary supplement for cardiovascular support and circulation [1.5.6]. | Medically supervised prevention of cardiovascular events like heart attack and stroke in at-risk individuals [1.4.2]. |
| Bleeding Risk | A primary concern, especially when combined with other blood thinners [1.2.4]. | A well-known side effect, including risk of gastrointestinal bleeding and hemorrhagic stroke [1.3.2]. |
| Regulation | Regulated as a dietary supplement in the U.S., meaning it is not subject to the same rigorous testing as prescription drugs [1.3.1]. | FDA-approved over-the-counter and prescription medication with established dosing and safety profiles. |
| Other Effects | May lower blood pressure [1.5.2]. | Can cause stomach irritation and ulcers. |
Conclusion
While nattokinase shows promise as a supplement for supporting cardiovascular health, its negative side effects are significant and should not be overlooked. The primary risk is excessive bleeding, which is amplified when taken with anticoagulant or antiplatelet medications. It may also cause an unsafe drop in blood pressure when combined with antihypertensive drugs. Due to these risks and a lack of long-term safety data, it is crucial to consult with a healthcare professional before taking nattokinase, especially if you have any pre-existing health conditions or are taking other medications. Self-substituting prescribed medications like warfarin with nattokinase can have severe consequences [1.3.3].
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