Opposes drug effect
DO NOT supplement without prescriber supervision if on warfarin.
Not Prohibited.
Independently graded against 178,763 indexed supplements and 757 reviewed supplement and medication pairs, sourced from PubMed, FDA CAERS, openFDA, and NIH DSLD | Last updated: August 24, 2026
Not medical advice. Based on published clinical research and systematic reviews.
Safety
Warfarin (Coumadin)
MK-7 supplementation may reduce warfarin effectiveness more than equivalent K1 dose due to longer tissue retention. INR monitoring required when starting or stopping MK-7.
MK-7 is more potent INR-lowering than K1 at similar doses. Avoid initiating without prescriber awareness.
Vitamin K2 menaquinone-7 has long half-life and accumulates more than K1. Even modest MK-7 doses (45 to 180 mcg per day) can antagonize warfarin and lower INR.
High-dose vitamin K1 supplementation (over 100 mcg per day) can reverse warfarin anticoagulation, reducing INR and increasing thrombosis risk. Inconsistent vitamin K intake causes INR fluctuations. Standard advice: maintain consistent daily vitamin K intake; avoid high-dose vitamin K supplements unless prescribed for warfarin reversal.
Vitamin K1 directly antagonizes warfarin. Avoid high-dose vitamin K supplements (over 100 mcg) without prescriber guidance. Maintain consistent vitamin K dietary intake to stabilize INR.
Vitamin K1 (phylloquinone) is the direct substrate antagonized by warfarin. Warfarin inhibits VKORC1 to prevent vitamin K recycling. Exogenous vitamin K1 directly reverses warfarin anticoagulation.
Decreased sensitivity to warfarin, leading to lower INR and a requirement for higher maintenance doses of warfarin to achieve adequate anticoagulation.
Vitamin K directly antagonizes the pharmacodynamic effect of warfarin, which acts as a vitamin K antagonist by inhibiting the vitamin K epoxide reductase complex, thereby overcoming the drug's inhibition of vitamin K-dependent clotting factor synthesis.
Educational information only. This is not medical advice. These statements have not been evaluated by the FDA. Talk to your prescriber before starting, stopping, or combining any supplement with prescription medication.