Many patients using warfarin also take aspirin

Clinical Question

What are community patterns of practice and outcome regarding the combination of warfarin and an antiplatelet agent?

Bottom Line

The combined use of aspirin with warfarin is common, but this combination is not supported by the evidence and it increases the risk of hemorrhage. Physicians should ask patients who take warfarin about their use of aspirin products and should discourage the combination. (LOE = 2b)


Johnson SG, Rogers K, Delate T, Witt DM. Outcomes associated with combined antiplatelet and anticoagulant therapy. Chest 2008;133(4):948-954.  [PMID:18198244]

Study Design

Cohort (retrospective)


Unknown/not stated




The combination of anticoagulation using warfarin and an antiplatelet agent (aspirin, clopidogrel, or dipyridamole) is only recommended for selected patients with mechanical heart valves. Although it has been studied in patients after acute myocardial infarction, no benefit was seen, and the risk of hemorrhage was higher (Circulation 2002;105;557-563; POEM #40656). This cohort study examined the records of patients in the Kaiser Permanente system cared for by their coagulation service as of September 30, 2005. Patients who reported the use of aspirin or who had been prescribed dipyridamole or clopidogrel during the previous 90 days were considered antiplatelet users (n = 1623) and the remainder were considered nonusers of antiplatelet agents (n = 2560). The vast majority were taking aspirin, usually in a dose of 81 mg per day. Only 1.3% of patients taking warfarin were also taking clopidogrel. The primary indications for anticoagulation in the combined therapy group were atrial fibrillation (47.7%), venous thromboembolism (17.3%), valvular heart disease (12.6%), stroke or transient ischemic attack (8.3%), coronary artery disease (6.5%), cardiomyopathy (3.7%), and arterial thromboembolism (1.5%). Combination therapy was less common among patients being treated for venous thromboembolism, but more common among those with coronary artery disease, cardiomyopathy, or cerebrovascular disease as the primary indication. Adjusted odds ratios showed a greater risk of any hemorrhage (2.7; 95% CI 1.4 - 5.3) and major hemorrhage (2.1; 95% CI 1.01-4.4) with combination therapy, but no difference in the risk of death, thrombosis, or coronary events. International normalized ratio control was a secondary outcome, and was worse in the combination therapy group.