Nattokinase is an enzyme extracted from Natto, a traditional Japanese food made by fermenting soybeans. It's commonly sold as a dietary supplement and is most often marketed for heart and circulatory health. What it's claimed to do Research has explored nattokinase for: Supporting healthy blood flow Breaking down fibrin (a protein involved in blood clot formation) Mildly lowering blood pressure in some people Supporting cardiovascular health What the evidence says The evidence is promising but not definitive. Some small clinical studies have found: Blood pressure: A modest reduction (around 3–5 mmHg in some people with mildly elevated blood pressure). Blood clotting: It appears to have fibrinolytic (clot-dissolving) activity in laboratory and some human studies, but it should not be considered a substitute for prescription blood thinners. Cholesterol: May help lower bad cholesterol