MajorVitamin K1, haemostatic, antidote for coumarin anticoagulant overdose×Vitamin K antagonist anticoagulants
Updated · Methodology
Mechanism
Warfarin works precisely by antagonising vitamin K: it blocks the recycling that activates factors II, VII, IX and X. Giving vitamin K1 reverses the drug directly. NIH ODS describes this as a serious and potentially dangerous interaction and stresses that consistency is what matters: sudden changes in intake, in either direction, destabilise the INR.
Symptoms
Adding vitamin K drops the INR below range and thrombotic risk returns: leg pain and swelling, sudden breathlessness, neurological deficit. Stopping it abruptly does the reverse, with a high INR, bleeding gums, bruising and dark urine.
Management
Do not add vitamin K to warfarin therapy on your own. Anyone already taking it should not stop abruptly: the aim is steady intake, leafy greens included, with more frequent INR checks during the first weeks of any change. Vitamin K1 as an antidote in overdose is handled in hospital and has nothing to do with the daily supplement.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.
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Sources
- NIH Office of Dietary Supplements: Vitamin K – Health Professional Fact Sheet (2025)– NIH ODS, Vitamin K, Warfarin and similar anticoagulants
- AEMPS: Ficha técnica: Warfarina (Aldocumar 5 mg) (nº registro 63064), sección 4.5 (2023)– AEMPS, CIMA, nº registro 63064, revisión 01/2023, sección 4.5
- AEMPS: Ficha técnica: Fitomenadiona (nº registro 27262), sección 4.5 (2023)– AEMPS, CIMA, nº registro 27262, revisión 10/2023, sección 4.5