Pharmacogenomics offers substantial hope for improved care of patients taking warfarin. One group estimated that formally integrating genetic testing into routine warfarin therapy in the US could result in the avoidance of 85,000 serious bleeding events and 17,000 strokes annually with a cost savings of over $1 billion annually. Common single nucleotide polymorphisms (SNPs) in the gene encoding Vitamin K Epoxide Reductase (VKOR) substantially affect one's sensitivity to warfarin, mediating a doubling or halving of the dose required for optimal anticoagulation. Warfarin inhibits clotting by inhibiting the enzyme VKOR, and thus inhibiting vitamin K dependent clotting factors. A number of recent retrospective studies have shown that polymorphisms in the VKOR gene may account for 20-30% of the variance in warfarin dose seen in patients on stable, long-term warfarin therapy.