Vitamin K is a fat-soluble vitamin essential for blood clotting, bone metabolism, and vascular health. K1 (phylloquinone) comes from leafy greens; K2 (menaquinone) comes from fermented foods and meat. Our research, from 24 RCTs, 13 meta-analyses, and 30,302 participants, shows it improves bone mineral density markers. The critical safety fact: vitamin K directly counteracts warfarin. If you're on blood thinners, vitamin K supplementation without medical supervision is dangerous.
Counteracts drug effect
DO NOT supplement without doctor supervision if on warfarin.
Not Prohibited.
Reviewed by the Scan Dose Research Team and Clinical Advisory Board | Last updated: April 5, 2026
Not medical advice. Based on published clinical research and systematic reviews.
Safety
Vitamin K is the direct pharmacological antagonist of warfarin. Supplementing without cardiology supervision can cause dangerous clots.
Dangerous interactions. Talk to your prescriber before using this supplement if you take any of these.
Warfarin (Coumadin)
Vitamin K reactivates clotting factors II, VII, IX, and X, directly opposing warfarin.
Source: FDA label, clinical standard
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.