Finally Question #3 as to why oral anticoagulation therapy is underutilized concerns the difficulties with use of warfarin, the anticoagulant drug that has been in clinical use for the longest time.  The well-known difficulties with warfarin are the very narrow therapeutic window, the multiple drug and food interactions, and finally there are genetic variations that make the use of warfarin quite difficult. 

Rothman SA. Am J Med 2013; 126: 00-00.