Vitamin K and Warfarin
Supplement–drug interaction evidence from the TruthStack database.
| Severity | CRITICAL |
|---|---|
| Evidence Tier | Moderate |
| Interaction Type | ANTAGONISTIC |
| Mechanism | PHARMACODYNAMIC |
| Last Reviewed | 2026-02-15 |
Summary
Vitamin K directly opposes warfarin mechanism. Warfarin works by blocking vitamin K-dependent clotting factor synthesis. Supplemental vitamin K restores clotting causing therapeutic failure with stroke and embolism risk. DO NOT SUPPLEMENT without physician direction. Even greens powders contain enough vitamin K to destabilize INR.
Higher-Concern Contexts
This interaction may be of particular concern in the following contexts:
- anticoagulant use
API Reference
GET https://api.truthstack.co/v1/check?c1=vitamin%20k&c2=warfarin
Open, unauthenticated. Returns JSON. Developer documentation
Related Interactions
What this page is and is not. TruthStack is an informational reference database that describes published pharmacological findings. It does not provide medical advice, diagnosis, or treatment recommendations. The information on this page reflects flags in our database and should not replace consultation with a qualified healthcare provider. Always discuss supplement-drug combinations with your prescriber or pharmacist.