The pharmacology of warfarin is complex and the therapeutic window is narrow, so how to use warfarin correctly has become a difficult problem for clinicians. Many factors can affect the efficacy of warfarin. In addition to genetic, dietary and disease factors, drug interactions are also important factors affecting the efficacy. Warfarin itself is known to inhibit hepatic cyclo-oxidoreductase, which prevents the reduction of inactive oxidized vitamin K (VK) to active reduced VK, prevents the circulating application of VK, interferes with the carboxylation of VK-dependent coagulation factors II, VII, IX and X, and prevents their activation for anticoagulation purposes. Warfarin is rapidly absorbed in the gastrointestinal tract with a half-life of 36-42 hours, bound to plasma proteins, and stored in the liver. It is almost completely metabolized by the liver. There are two types of drugs that interact with warfarin, which can enhance or diminish the effect of the drug, respectively. Understanding these drugs can better know the clinical use of drugs. I. Drugs that enhance the effect 1. Some drugs have a stronger affinity for plasma proteins than warfarin, which increases the free warfarin and enhances the anticoagulant effect. This type of drugs are: aspirin, bactrim, methotrexate, clobetasol, sulfonamides, propofol, etc. 2, drugs through the inhibition of liver microsomal enzymes, can make the metabolism of warfarin reduced and increase the effectiveness. This class of drugs are: chloramphenicol, allopurinol, metronidazole, cimetidine, monoamine oxidase inhibitors. 3, reduce VK absorption and affect thrombinogen synthesis can also enhance the effectiveness of warfarin. These drugs are: azithromycin, erythromycin, clarithromycin, doxycycline, cephalosporins, nalidixic acid, ciprofloxacin, norfloxacin, ofloxacin, etc. 4.Promote the binding of warfarin to receptors: quinidine, levothyroxine, phenylephrine. 5.Interfere with platelet function, make warfarin anticoagulation more obvious: salicylates, paracetamol, chlorpromazine, benadryl, etc. 6, drugs with thrombolytic or anticoagulant effect: streptokinase, urokinase, heparin, etc. Drugs that weaken the effect 1.Inhibit the absorption of warfarin: acid inhibitors, laxatives, ashwagandha, etc. 2.Increase the synthesis of microsomal enzymes in the liver: Antipyrine, carbamazepine, barbiturate, pentobarbital, phenobarbital, isopentobarbital, isobutyric acid, rifampin, etc. 3.Promote the synthesis of coagulation factor II, VII, IX, X: oral contraceptives, estrogen, VK, etc.