•Omeprazole is a proton pump inhibitor that decreases gastric acid secretion. When combined with warfarin, omeprazole can actually prolong elimination and increase INR. •Omeprazole has not been shown to cause encephalopathy when mixed with warfarin. •Although omeprazole inhibits the absorption of many drugs, it actually increases the effects of warfarin. •Omeprazole should be taken before breakfast, once a day (it has a 72 hour duration, 50% efficacy after 24 hours). •Warfarin should be taken the same time everyday, usually in the evening or at bedtime.