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Coumadin (warfarin) will lose its effects at varying rates, depending on dietary factors, liver function, and other medicines that are being taken. If blood Coumadin levels are in the therapeutic range, in most people the effects are gone within 3-4 days of stopping the medicine. If the Coumadin levels are too high (a toxic level), or a person needs urgent reversal of the drug (due to bleeding or a need for surgery), the effects can be reversed with injection of certain medicines to reverse the effects.
Medically reviewed by John A. Daller, MD; American Board of Surgery with subspecialty certification in surgical critical care
"Warfarin and other VKAs: Dosing and adverse effects"