Nattokinase, a large enzyme of the serine protease family, is isolated from the fermented food product known as nattō (boiled soybeans fermented with the bacterium Bacillus subtilis). Interest in using nattokinase as a supplement has grown because of its cardiovascular benefits of reducing blood clotting and blood pressure.[1][2][3] Although there’s some concern of an increased bleeding risk, reports of bleeding have been very rare and limited to people with chronic conditions or who are already taking blood thinning medications.[4][5]