Warfarin is the most commonly used anticoagulant for patients with atrial fibrillation, valvular disease, and deep vein thrombosis, and is inexpensive and effective for sure. However, there are many factors that can affect the anticoagulant effect of warfarin, and it is a very delicate drug. Patients with individual differences in the efficacy of the drug, therefore, it is necessary to adjust the dose of the drug at any time according to the results of coagulation-related laboratory tests, such as the international normalized ratio (INR), if there is no condition to monitor the coagulation-related test indicators, then the patient should not use warfarin, otherwise it may cause serious consequences such as bleeding, or even life-threatening. After the INR is maintained at 2,0~3,0, the number of tests can be gradually reduced and the test interval gradually extended to 3 days, 1 week, 2 weeks, or even 4 weeks. In case of cumulative overdose or underdose during warfarin use, the dose should be fine-tuned at any time. Monitoring should be done in the coagulation laboratory of the same hospital. 1. The main adverse effect of warfarin is bleeding, most commonly epistaxis, gum bleeding, skin petechiae, hematuria, uterine bleeding, blood in the stool, bleeding from wounds and ulcers, etc. Do not use this product casually when there is no condition to measure prothrombin time or prothrombin activity to prevent overdose causing hypoprothrombinemia and resulting in bleeding. If prothrombin time exceeds 2.5 times normal (normal value is 12 seconds), prothrombin activity drops to less than 15% of normal value or bleeding occurs, the drug should be discontinued immediately. In severe cases, vitamin K can be used orally (4-20 mg) or slowly injected intravenously (10-20 mg), and the prothrombin time can be restored to a safe level 6 hours after the drug is administered. If necessary, fresh whole blood, plasma or prothrombin complex can also be input. 2.Patients with bleeding tendency, such as hemophilia, thrombocytopenic purpura, severe liver and kidney disease, active peptic ulcer, brain, spinal cord and ophthalmic surgery patients are prohibited. 3.The following conditions should be used with caution: cachexia, debility, fever, chronic alcoholism, active tuberculosis, congestive heart failure, severe hypertension, subacute bacterial endocarditis, menorrhagia, preterm abortion, etc. 4. During the long-term application of the minimum maintenance dose, if surgery is required, vitamin K1 injection 50mg can be administered sedately, but the drug should be discontinued before performing central nervous system and ophthalmic surgery. After gastrointestinal surgery, fecal occult blood should be checked. 5. Acetylsalicylic acid, pautazone. Hydroxy pauterisone, chloral hydrate, disulfiram, diuretic acid, quinidine, methanesulfonate material, clobetanil anti-inflammatory pain, methomylate, quinine, anabolic hormones, tetracyclines, sulfonamides, etc., can enhance their anticoagulant effect, thus increasing the bleeding tendency. 6, Phenobarbital, Grumet and phenytoin sodium can accelerate the metabolism of this product and weaken its anticoagulant effect.