Warfarin is a bicoumarin anticoagulant that inhibits thrombosis by affecting the metabolism of VitK. It is commonly used in clinical practice in patients with atrial fibrillation, pulmonary embolism, and venous thrombosis of the upper and lower extremities. Because the anticoagulant effect of warfarin varies greatly among individuals and is easily affected by other drugs, the International Normalized Ratio (INR), which is an indicator of its anticoagulant effect, fluctuates greatly in the early stage of administration, and overdose of warfarin may cause bleeding complications. The INR should be controlled and stabilized at 1.6 to 2.5 (European and American guidelines usually recommend stabilization at 2.0 to 3.0). The doctor will adjust the dose of warfarin according to the value of INR. After the INR is within the standard range (1.6-2.5) for 2-3 consecutive times, the INR can be tested every 1 week at the hospital, and if the INR meets the standard continuously, the INR can be extended to 1 time every month after 1 month. In addition, patients taking warfarin If patients experience bleeding from nose, gums, mouth, eyes, urine, stool, severe headache, vomiting (intracranial hemorrhage) and other signs of bleeding while taking warfarin, they should go to the hospital for INR testing and corresponding treatment.