Believe it or not, Nattokinase has no side effects. Boiled soybeans are fermented to produce Nattokinase. It is a proteolytic enzyme and it is a natural ingredient. It has several health benefits which can help decrease the risk of heart attacks and stroke. Most people are not aware that a single blood clot can potentially cause severe damage to your cardiovascular system. Any blockage in your arteries can diminish the supply of oxygen in other parts of the body. Nattokinase is more effective in dissolving cholesterol, fibrinogen and plaque deposits when consumed in-between meals. Since Nattokinase breaks down proteins, one must avoid taking it with meals. It will just focus on dissolving the proteins in our stomach instead of being circulated in the blood stream to digest the blood clots. There is no such thing as Nattokinase side effects but it is best to consult a doctor first if you are already taking other blood thinning products.