Warfarin is affected by dietary and drug interactions, and almost all enzymes metabolized by hepatic cytochrome P450 interact with warfarin; the international normalized ratio (INR) should be monitored more closely when adding or discontinuing any drug. Some drugs, such as abciximide, inhibit the absorption of warfarin; pautazone, phenylsulfonazone, and pyrazolone displace warfarin from its plasma protein binding site and increase its blood concentration; vincristine reduces the absorption of vitamin K due to inhibition of vitamin K-producing bacteria in the intestine, which hinders the synthesis of coagulation factors; mecamylguanidine and methotrexate inhibit the metabolism of warfarin; barbiturates, rifampin, and ashwagandha cause warfarin metabolism is accelerated. Drug-warfarin interactions are classified into four classes according to the degree of sufficiency of clinical evidence. The drugs that should be given the most attention in combination with warfarin are aspirin and NSAIDs, both of which increase the risk of warfarin bleeding because of inhibition of platelet function. Aspirin and NSAIDs also corrode the gastric mucosa, further increasing the chances of upper gastrointestinal bleeding. Even low doses of aspirin (75 to 100 mg/d) combined with moderate or low strength warfarin may increase the risk of bleeding. Even with an INR as low as 1.5, the combination of aspirin increases the incidence of bleeding in patients on anticoagulation therapy. Akins reported the results of SPORTIFIII and SPORTIFV at the 2005 Annual Stroke Conference, two studies that together included more than 7000 patients with AF who had already had 1 stroke or TIA, which compared the effectiveness of the new anticoagulant Ximelegatran with warfarin for stroke prevention [6, 7]. The investigators found that when aspirin was combined with anticoagulants, the annual event rate increased from 2.5% to 3.8% in the Ximelegatran group; and from 2.9% to 5.1% in the warfarin group. A multifactorial risk analysis showed a hazard ratio of 0.78 when the two anticoagulants were applied alone, compared with 1.68 when aspirin was added. therefore, Professor Diener, one of the organizers of the SPORTIF series of studies, stated that the combination of aspirin and oral anticoagulants is not recommended except in patients with very high-risk coronary artery disease. One third of patients with atrial fibrillation have combined coronary artery disease, and these patients are at risk of both stroke and cardiovascular events. If a patient is already on anticoagulation therapy, is it necessary to combine aspirin to prevent cardiovascular events? There are no clinical trials to answer this question. Previous clinical studies comparing the effect of adding aspirin 75-100 mg/d to anticoagulation therapy (INR 2.0-2.5) on the prevention of coronary events have found a limited effect of the addition of aspirin and an increased incidence of minor bleeding. The fact that patients enrolled in clinical trials completed in patients with coronary artery disease were on average 10 years younger than patients with atrial fibrillation does not necessarily mean that similar results were seen in patients with atrial fibrillation. In stroke prevention trials in atrial fibrillation comparing the effects of aspirin and warfarin therapy, warfarin alone was better at preventing coronary heart disease and ischemic stroke than aspirin alone. It can be inferred from these studies that moderate-intensity anticoagulation therapy may provide adequate protection against coronary events. The addition of aspirin has the potential to further reduce cardiovascular events, but certainly increases bleeding complications. The American College of Chest Physicians 7th Antithrombotic Society (ACCP7) concluded that concurrent moderate-intensity anticoagulation and aspirin is also acceptable in patients with atrial fibrillation in combination with coronary artery disease.