K2 also reverses warfarin's effect
MK-4 and MK-7 forms of vitamin K2 can interfere with warfarin. MK-7 has a longer half-life (~3 days) and may cause more sustained INR changes than K1. Even low doses can affect clotting.
Avoid vitamin K2 supplements on warfarin. If prescribed, requires frequent INR monitoring.
Avoid combination entirely
K2 also reverses warfarin's effect. Avoid vitamin K2 supplements on warfarin. If prescribed, requires frequent INR monitoring.
Avoid combination entirely
This interaction is rated “Danger” by Formulate. MK-4 and MK-7 forms of vitamin K2 can interfere with warfarin. MK-7 has a longer half-life (~3 days) and may cause more sustained INR changes than K1. Even low doses can affect clotting.
Studies from our registry that mention vitamin k2 or warfarin. Each links to the primary source and the other Formulate pages citing it.
Mentions warfarin · 2025
Impact of Ginkgo biloba drug interactions on bleeding risk and coagulation profiles
Primary literature · Observational study
Ginkgo + aspirin: bleeding risk OR 1.12 (95% CI 1.07-1.18, p<0.001); abnormal coagulation OR 1.48 (95% CI 1.32-1.66, p<0.001). Ginkgo + clopidogrel: bleeding risk OR 1.10 (95% CI 1.05-1.15, p<0.001); abnormal coagulation OR 1.58 (95% CI 1.40-1.77, p<0.001). Ginkgo + warfarin: NO statistically significant correlation with bleeding or coagulation.
Mentions vitamin k2 · 2017
Menaquinone-7 supplementation improves arterial stiffness in healthy postmenopausal women
Knapen et al. · Thrombosis and Haemostasis
180mcg/day MK-7 for 3 years significantly improved arterial stiffness in postmenopausal women.
Mentions warfarin · 2016
Interaction Between Dietary Vitamin K Intake and Anticoagulation by Vitamin K Antagonists: Is It Really True? A Systematic Review
Violi et al. · Medicine (Baltimore)
Conflicting evidence on whether dietary vitamin K intake affects warfarin response. Some studies show inverse correlation between vitamin K intake and INR changes. Others suggest a minimum vitamin K intake is REQUIRED for stable anticoagulation. Conclusion: available evidence does NOT support the old advice to restrict dietary vitamin K when starting warfarin. Consistency of intake matters more than absolute level.
Mentions warfarin · 2015
Ginkgo and Warfarin Interaction in a Large Veterans Administration Population
Millery et al. · AMIA Annu Symp Proc
Hazard ratio for bleeding adverse event with concurrent ginkgo + warfarin: 1.38 (95% CI 1.20-1.58, p<0.001).
Mentions warfarin · 2015
Interaction between warfarin and Chinese herbal medicines
Lin et al. · Stat Med
Dong quai listed among Chinese herbal medicines with documented warfarin potentiation via PD mechanism. Recommends caution when combining.
Mentions warfarin · 2014
Warfarin Interactions with Medicinal Herbs
Primary literature · Systematic review
Dong quai contains natural coumarin derivatives (ferulic acid, osthole) with documented antithrombotic and platelet-inhibitory effects. Animal steady-state studies show dong quai significantly increased prothrombin time WITHOUT affecting warfarin concentration - suggesting pharmacodynamic (not pharmacokinetic) interaction. Recommends informing patients of the potential hazard.
Other interactions to know
Salvia miltiorrhiza potentiates warfarin
Vitamin K directly antagonizes warfarin. Consistency of intake, not avoidance, is the right clinical approach.
Fish oil may increase bleeding risk with warfarin
High-dose vitamin E increases warfarin bleeding risk
Garlic supplements increase bleeding risk
Dong quai contains natural coumarins and has potentiated warfarin in a published case, raising bleeding risk.
Ginger may enhance anticoagulant effect
Vitamin D and K2 work synergistically
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Medical disclaimer. This page is for educational purposes only and does not replace advice from a qualified healthcare provider.
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