From the Guidelines
Vitamin K2 supplementation can significantly affect warfarin/Coumadin levels, and patients on warfarin therapy should avoid starting or stopping any vitamin K supplements without consulting their healthcare provider. Vitamin K2 directly counteracts the anticoagulant effects of warfarin, which works by inhibiting vitamin K-dependent clotting factors. Taking K2 supplements while on warfarin can reduce the medication's effectiveness, potentially increasing the risk of blood clots and decreasing INR (International Normalized Ratio) values 1.
Key Considerations
- The American College of Chest Physicians evidence-based clinical practice guidelines suggest that vitamin K1 (phytonadione) is the preferred form of vitamin K for reversing warfarin anticoagulation, and vitamin K2 (menaquinone) has not been well studied in clinical trials 1.
- A consistent daily intake of vitamin K through diet is recommended, as sudden changes in vitamin K consumption can destabilize anticoagulation control 1.
- If a patient needs to take vitamin K2 for another health reason while on warfarin, their doctor will need to adjust their warfarin dosage accordingly and monitor their INR more frequently to ensure proper anticoagulation.
Management Strategies
- Patients with supratherapeutic INR values (above 4.5) without bleeding may be managed with withholding VKA, adjusting the dose of VKA, or providing some dose of vitamin K 1.
- The use of vitamin K2 supplementation in patients on warfarin therapy requires careful consideration of the potential benefits and risks, and should only be done under the guidance of a healthcare provider 1.
From the Research
K2 Supplementation and Warfarin/Coumadin Levels
- The effect of K2 supplementation on warfarin/coumadin levels is a topic of interest in the medical community, with several studies investigating this interaction 2, 3, 4, 5, 6.
- A case report published in 2025 found that prophylactic continuous menaquinone-4 (vitamin K2) injections administered to a patient who had ingested a large amount of warfarin helped prevent severe coagulopathy and bleeding 2.
- A systematic review published in 2014 found that low-dose vitamin K supplementation may improve anticoagulation control in patients taking warfarin, but the evidence was limited and inconclusive 3.
- An animal study published in 1999 found that high doses of vitamin K2 reduced the effect of warfarin on thrombosis, but did not enhance the occurrence of thrombosis more than that without warfarin treatment 4.
- A study published in 2024 found that oral vitamin K was effective in correcting supratherapeutic INR levels in non-bleeding outpatients taking warfarin, with a low rate of bleeding complications 5.
- Another study published in 2010 found that a single 2.5 mg dose of oral vitamin K was effective in treating INR values in excess of 10 in patients taking warfarin, with a low rate of major bleeding 6.
Key Findings
- Vitamin K2 supplementation may interact with warfarin and affect its anticoagulant activity 2, 4.
- Low-dose vitamin K supplementation may improve anticoagulation control in patients taking warfarin, but more research is needed to confirm this finding 3.
- Oral vitamin K is effective in correcting supratherapeutic INR levels in non-bleeding outpatients taking warfarin, with a low rate of bleeding complications 5, 6.