Natto is high in vitamin K₂, a blood coagulant, and its consumption is restricted for cardiovascular disease patients taking warfarin. In fact, the study, in which normal subjects received warfarin and consumed 100g of natto (one large packet of commercially available natto) after their thrombotest values decreased, showed that the high thrombotest level persisted for 24 to 72 hours and the blood was easy to coagulate, even though warfarin was continuously administered(Summary of Clinical Study②）。

On the other hand, when Nattokinase was taken with warfarin, clinical symptoms and various biochemical tests showed that there were no particular side effects and the values of blood components related to blood coagulation fluctuated less（Summary of Clinical Study ①）. The results of this study strongly suggest that an appropriate dose of Nattokinase with warfarin has a stable and effective effect on the coagulation-fibrinolytic system (thromboprophylaxis) and is highly safe.