What are adverse effects of warfarin?

Bleeding disorders: The principal adverse reaction caused by warfarin treatment is hemorrhage. Therefore, it is important to frequently monitor (INR) and adjust the anticoagulant effect. Minor bleeding may be treated by withdrawal of the drug and administration of oral vitamin K; Severe bleeding requires that greater doses of the vitamin K be given intravenously. Whole blood, frozen plasma, or plasma concentrates of the blood factors may also be employed to arrest hemorrhage.