Nattokinase Side Effects
Health Benefits

Nattokinase Side Effects: What You Should Know

on Nov 11, 2023| Modified on Feb 21, 2024
Nattokinase side effects.

Nattokinase, an enzyme derived from natto, a traditional Japanese fermented soybean dish, has gained traction as a natural health supplement. Celebrated for its heart health benefits and role in improving blood circulation, it’s vital to explore nattokinase's side effects for informed and safe use.

What is Nattokinase?

This enzyme, sourced from fermented soybeans, is known for its capacity to break down blood clots, which may reduce heart disease and stroke risks. However, its soybean base can be a concern for those with soy allergies.

Nattokinase and Blood Clotting

  1. Decreased Blood Clotting and Increased Bleeding Risks: Nattokinase can reduce blood clotting, potentially leading to increased chances of bruising and bleeding. This effect is significantly pronounced when nattokinase is taken alongside medications that slow clotting, such as aspirin, ibuprofen, and other blood thinners. This combination can cause excessive bleeding and bruising​​​.1,2
  2. Worsening of Bleeding Disorders: Nattokinase acts like a blood thinner and might exacerbate bleeding disorders. People with such conditions should use nattokinase with caution. Additionally, those undergoing surgery should be aware that nattokinase might increase the chance of bleeding during and after the procedure.3
  3. Interactions with Blood-Thinning Medications: There is a noted risk of increased bleeding when nattokinase is used in conjunction with blood-thinning drugs. For example, a case report highlighted a patient who had to undergo a repeat valve replacement surgery after replacing warfarin with nattokinase for an extended period. Another report mentioned internal bleeding leading to death in an elderly woman who took over-the-counter nattokinase for an irregular, rapid heartbeat.4

Common Side Effects

The consumption of nattokinase may lead to several side effects, especially when taken in inappropriate doses. These include:

  • Gastrointestinal Issues: Reports of bloating, gas, and upset stomach are common.
  • Allergic Reactions: Being derived from soy, nattokinase can trigger allergic responses in sensitive individuals.
  • Heightened Bleeding Risk: Its blood-thinning properties can increase bleeding, particularly for those with bleeding disorders or on anticoagulant drugs.
  • Lowered Blood Pressure: It may cause a drop in blood pressure, a concern for those on blood pressure medication or with naturally low levels.
  • Dizziness and Light-headedness: These symptoms might occur, especially at high doses or in sensitive users.
  • Muscle Pain and Tenderness: Unexplained muscle discomfort has been reported.
  • Supplement Interactions: Nattokinase can interact with other blood-thinning supplements, amplifying their effects.
  • Liver Function Impact: High doses might affect liver function, requiring monitoring in individuals with liver conditions.

Special Precautions for Specific Groups

Certain groups need to exercise extra caution:

  • Pregnant and Breastfeeding Women: The effects of nattokinase during pregnancy and breastfeeding are not well-studied, necessitating caution.
  • Pre and Post Surgery: Due to its blood-thinning effects, nattokinase should be discontinued prior to any surgical procedures to prevent excessive bleeding.

Potential Liver Side Effects

The liver plays a vital role in processing and detoxifying substances that enter the body, including supplements like nattokinase. Although nattokinase is considered safe for most people when used in moderation, there is a theoretical concern that its effects on blood clotting could impact liver function, particularly in individuals with liver disorders. Here are some considerations:

  1. Liver Enzyme Elevations: Any supplement or medication metabolized by the liver has the potential to cause changes in liver enzyme levels, indicating stress or damage to liver cells. While no widespread evidence suggests that nattokinase directly causes significant liver enzyme elevations, individuals with existing liver conditions should be cautious.
  2. Impact on Hemostasis: The liver is also involved in producing clotting factors, and since nattokinase can influence clotting mechanisms, there's a hypothetical risk that it could affect liver-related hemostasis, especially in those with liver disease that predisposes them to bleeding complications.

Be alert to symptoms that could indicate liver issues, such as fatigue, weakness, abdominal pain, jaundice, and dark urine. If you experience these symptoms while taking nattokinase, seek medical advice promptly.


The potential side effects of nattokinase underscore the importance of proceeding with caution when considering nattokinase supplements, particularly for individuals with pre-existing health conditions or those on medication. It is always advisable to consult with a healthcare professional before starting any new supplement regimen.

Related Links:

Health Benefits of Nattokinase: Evidence-Based Findings
High-Dose Nattokinase: A Game-Changer for Atherosclerosis