Warfarin is an anticoagulant, belonging to the coumarin class of anticoagulants, which can mainly counteract the action of vitamin K in vivo, and can inhibit the synthesis of coagulation factors II, VII, IX, and X involved in vitamin K in the liver, but does not have any resistance to the coagulation factors II, VII, IX, and X already in the blood, and therefore cannot be used for anticoagulation in vitro. Therefore, warfarin cannot be used for anticoagulation in vitro. In addition, in vivo anticoagulation can only be effective after the active coagulation factors have been consumed. Warfarin has no significant anticoagulant effect at the beginning of the medication and needs to wait for a period of time, 3-5 days, before it can exert a better anticoagulant effect. Warfarin is also a big individual differences in the drug, in the use of the process must follow the doctor’s instructions, it is recommended to use in accordance with the recommended dosage, and in the process of using the drug should pay attention to monitoring the coagulation index.