In recent years, the clinical use of warfarin, a traditional anticoagulant, has increased as awareness of the dangers of nonvalvular atrial fibrillation and deep vein thrombosis has grown. Since many drugs (including over-the-counter medications) and foods can significantly affect the anticoagulant effect of warfarin, patients treated with warfarin should try to avoid or minimize the combination of drugs. When their use is necessary, intensive monitoring of coagulation should be performed. Many prescription or over-the-counter medications can enhance or diminish the effects of warfarin. Patients should be aware of this when taking warfarin so that improper use of the drug does not result in an increased risk of bleeding or thrombotic events. Drugs that may enhance the anticoagulant effect of warfarin: aspirin, sodium salicylate, indomethacin, prednisone, quinine, diuretic acid, methylsulfonylurea, metronidazole, allopurinol, erythromycin, chloramphenicol, some of the aminoglycoside antibiotics, cephalosporins, cimetidine, clofibrate, dexmethyltetramethasone, and ethylthiophthalaminophen. Drugs that reduce the anticoagulant effect of warfarin: phenytoin sodium, barbiturates, oral contraceptives, estrogens, colesevelam, rifampicin, vitamin K, chlorthiazepoxide, spironolactone, corticosteroids and so on. Drugs that cannot be combined with warfarin: epinephrine hydrochloride, amikacin, vitamin B12, mesalamine, oxytocin, chlorpromazine hydrochloride, vancomycin hydrochloride and so on. Some traditional Chinese medicines (e.g., Salvia miltiorrhiza, ginseng, Angelica sinensis, ginkgo, etc.) or foods (e.g., grapefruit, mango, garlic, ginger, onion, kelp, cauliflower, kale, carrots, etc.) may also enhance or weaken the anticoagulant effect of warfarin, which should also be noted in the process of medication. Patients should consult with their physicians and decide whether to have their coagulation function (mainly INR) tested or intervene as necessary after the application of the aforementioned medications or foods. Repeated coagulation tests are usually required in the early stages of drug administration. In patients with deep vein thrombosis, the prothrombin time is two to three times the normal value, and the international normalized ratio is between 2 and 3. After regularizing the dosage of the drug, the time for checking the coagulation index can be extended appropriately.