Pharmacist with pill bottles at computer
Jupiterimages/Stockbyte/Getty Images

Nattokinase is an enzyme that can be used to prevent blood clots that are associated with strokes and heart attacks. Heart disease is the No. 1 killer of Americans, while stroke is No. 3. Nattokinase is derived from the Japanese soy food called natto that somewhat resembles blue cheese. There are dangers associated with nattokinase, and you should not use it without the guidance of a health care provider.

Bleeding Risk

If you take nattokinase along with an anticoagulant like aspirin, coumadin or warfarin, it increases your risk of bleeding, including internal bleeding, says Dr. Ray Sahelian of Los Angeles, author of “Mind Boosters.” In one case, a person taking aspirin to prevent stroke along with 400 milligrams of nattokinase for seven days suffered an acute brain hemorrhage, says Y.Y. Chang, lead author for a case report from Taiwan’s Chang Gung Memorial Hospital that was published in the journal “Internal Medicine.” In addition to the hemorrhage, the person suffered multiple brain micro-bleeds, Chang notes.

Herb Interactions

Taking nattokinase along with herbs that have blood-thinning properties also raises your risk for bleeding or bruising. Herbs with anticoagulant properties include anise, angelica, bogbean, garlic, danshen, ginger, horse chestnut, turmeric, red clover, ginkgo biloba and white willow, according to “The Essential Herb-Drug-Vitamin Interaction Guide,” by George T. Grossberg and Barry Fox. Garlic and ginkgo biloba are among the most popular herbs on the market, the authors advise.


Nattokinase may be used to lower blood pressure, says Ji Young Kim, lead author for a study published in “Hypertension Research.” In theory, that means taking it along with other medicines that lower blood pressure such as acebutolol or quinapril increases the risk for hypotension, or excessively low blood pressure. Taking it with herbs that have this effect, such as black cohosh, also theoretically increases this risk.

Unknown Effects

Effects other than nattokinase’s ability to prevent thrombosis, or blood clotting, and potential for lowering blood pressure remain unknown as of 2010 due to lack of study, says Sahelian, so any significant side effects are not yet reported in medical literature. Human trials need to be conducted to determine the risks and benefits of treatment with this enzyme, says Sahelian, who suspects that nattokinase crosses the blood-brain barrier due to reports of brain hemorrhage. This enzyme prevents aggregation of your red blood cells. Nattokinase works by dissolving fibrin, which is a protein involved blood clotting. Fibrin creates a "mesh" along with platelets that forms a hemostatic plug, or clot.