⚠️ Mechanism
Vitamin K is required for synthesis of clotting factors II, VII, IX, X. Warfarin inhibits vitamin K epoxide reductase. Supplemental vitamin K directly antagonizes warfarin's anticoagulant effect.
📋 Effect
Reduced anticoagulant effect; increased thrombosis risk
💊 Management
Avoid vitamin K supplements >150mcg/day. Maintain consistent dietary vitamin K intake. Monitor INR closely with any changes.
Plain Language Summary
This combination is dangerous because Vitamin K supplements can directly counteract the effects of Warfarin. This makes the medication less effective at thinning your blood, which increases the risk of developing blood clots.
Source
FDA warfarin labeling; Holbrook AM et al. Ann Intern Med 2005
Supporting Research
Antiplatelet and anticoagulant agents for secondary prevention of stroke and other thromboembolic events in people with antiphospholipid syndrome
Anticoagulants (extended duration) for prevention of venous thromboembolism following total hip or knee replacement or hip fracture repair
Antiplatelet and anticoagulant agents for secondary prevention of stroke and other thromboembolic events in people with antiphospholipid syndrome
Direct factor Xa inhibitors versus low molecular weight heparins or vitamin K antagonists for prevention of venous thromboembolism in elective primary hip or knee replacement or hip fracture repair
Factor Xa inhibitors versus vitamin K antagonists for preventing cerebral or systemic embolism in patients with atrial fibrillation
Antiplatelet agents and anticoagulants for hypertension
Primary prophylaxis for venous thromboembolism in ambulatory cancer patients receiving chemotherapy
Factor Xa inhibitors versus vitamin K antagonists for preventing cerebral or systemic embolism in patients with atrial fibrillation
Medical Disclaimer: This interaction record is for informational and educational purposes only and does not constitute medical advice. Drug-supplement interactions can be dangerous. Always consult your healthcare provider or pharmacist before combining any supplement with prescription medications. Do not stop or change any medication without professional guidance.