Treatment with coumarin oral anticoagulants, such as warfarin, is effective antithrombotic therapy, but patients treated with these drugs are at significant risk of bleeding. The risk of haemorrhage increases with increasing intensity of anticoagulation and overanticoagulation is common. Reversal can be achieved by stopping the coumarin drug or administration of vitamin K, fresh frozen plasma or coagulation factor concentrates. However, there are surprisingly few studies defining the optimum dose of these products and there are no randomized studies comparing the relative benefit and risk of coagulation factor concentrates versus fresh frozen plasma. Guidelines for the management of overdose are based on level III and IV evidence and are, therefore, only grade B recommendations at best. Further studies are required to determine the most effective use of products and the dose required for safe reversal of overanticoagulation.