We conducted an extensive literature review to evaluate the appropriate use, route, and dose of vitamin K to reverse excessive anticoagulation. Issues such as sample size, study design, different patient populations, and various study end points confounded results. Of 18 studies published, 8 enrolled 229 patients to evaluate parenteral vitamin K administration. Nine studies with 288 patients evaluated oral administration, and only 2 retrospective studies (280 patients) compared routes of administration. Reductions in international normalized ratios at 24 hours ranged from 21-42%, 47-86%, 25-67%, and 40-75% for temporary warfarin discontinuation alone, and intravenous, subcutaneous, and oral routes of vitamin K administration, respectively. Methodologically weak studies and indeterminate results plague interpretation of the literature on vitamin K. In general, results of this review support current guidelines for reversing excessive warfarin anticoagulation. However, it is important to realize that the quality of literature on which these recommendations are based is poor and that optimal dose and route of vitamin K administration remain unclear. Large, well- designed, randomized, controlled trials are necessary to define optimum management strategies for excessively anticoagulated patients.