The objective of this study was to examine and evaluate the frequency of bleeding and serious drug interactions among patients with atrial fibrillation (AF) treated with oral anticoagulant [Warfarin]. A random sample of 59 patients from Al-Watni government hospital in Nablus with a principal or secondary discharge diagnosis of AF was identified. All drug and clinical data were abstracted from the patient's files. We excluded patients who were less than 65 years of age, or left the hospital against medical advice, and those whose AF was transient or could not be confirmed. Of the original 59 AF patients, 19 were cliagnosed who were discharged on Warfarin. The mean age for these patients was 71.7 years. Among the patients discharged on Warfarin, 94.7 % had one or more drug – drug interactions that could lead to increase risk of bleeding. Many patients discharged on Warfarin were having multiple interacting drugs. Patient counseling and follow-up monitoring are essential and should be carried out to minimize the risk of bleeding and other complications.