The Dangers of Nattokinase

Nattokinase, also known as natto extract, is an enzyme derived from fermented soybeans that some companies sell as a supplement meant to promote good cardiovascular health. It can have harmful side effects and may lead people with serious health conditions to undertreat their disease.


Nattokinase is an enzyme extracted from natto, a form of fermented soybeans created by boiling the beans and combining them with a certain kind of bacteria. Natto is cheese-like substance that is popular as a breakfast food in Japan. Nattokinase is an extract from natto that is often made into capsules and taken as a food supplement that is supposed to dissolve blood clots that can cause heart attacks and strokes.

Dangerous Side Effects and Drug Interactions

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Hemophiliacs and people with other disorders that interfere with blood clotting should not take nattokinase because of an increased risk for bruising and bleeding. Similarly, people with conditions associated with bleeding -- such peptic ulcer disease and cirrhosis of the liver -- should not take nattokinase. Avoid taking nattokinase before or after surgery, or if you are pregnant because the supplement may interfere with normal blood clotting.

Anyone taking blood-thinning medication -- such as warfarin, heparin, clopidogrel and enoxaparin -- should avoid taking nattokinase because it may interact with these drugs, causing them to be more or less effective.

Do Not Rely on Nattokinase

The potential benefits of nattokinase are unproven. There have been no conclusive clinical studies of its effectiveness for preventing or treating any medical conditions.

Some Blood Clots are Good

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Nattokinase supposedly works as a "fibrinolytic agent," something that dissolves blood clots, potentially preventing heart attacks and strokes. However, not all clots in the body are bad. Blood clots are formed by blood particles known as platelets, which join together when they encounter a tear or hole in a blood vessel. Clots essentially plug these holes and stop bleeding, both internal and external.

People at Risk of Dangerous Clotting

Blood clots can be dangerous, especially if they block healthy blood vessels and cut off blood flow to vital organs. People with certain genetic disorders, injuries that cause immobility, or who have suffered trauma to a blood vessel can be at increased risk for a dangerous clot. People with these conditions should consult with their doctor about how to reduce the risk for blood clots and take prescribed medications that have been proven effective for their condition. If these people also want to take nattokinase as an additional protection against clots, they should talk with their doctor about whether it is safe.