Warfarin is mainly used in the clinic to prevent and control thromboembolic diseases, such as thromboembolic phlebitis. 1. Warfarin is an oral anticoagulant drug of coumarin class, which can antagonize the action of vitamin K and inhibit the synthesis of coagulation factors 2, 7, 9 and 10, thus exerting anticoagulant effect. 2. The main adverse reaction of warfarin is bleeding, most commonly nosebleed, gum bleeding, wound bleeding. Gastrointestinal reactions such as nausea, vomiting, and diarrhea may also occur. Effects on the blood system include leukopenia and increased granulocytes. There is also the possibility of damage to liver function, resulting in increased aminotransferases and increased bilirubin. 3. It should be noted that INR level should be tested during the administration of warfarin and the dosage should be adjusted in time according to the result. Warfarin is contraindicated in patients who are allergic to warfarin, patients with bleeding tendency, patients with severe hepatic or renal insufficiency, patients within 3 days after surgery, and pregnant and lactating women should be cautious. If there is any discomfort, consult a doctor promptly and follow the doctor’s instructions.