Vitamin K antagonist
![Warning label on a tube of](/Images/godic/202412/21/Rattenvergifwaarschuwing_edit4230.JPG")
![Vitamin K2 (menaquinone). In menaquinone the side chain is composed of a varying number of isoprenoid residues.](/Images/godic/202412/21/Menaquinone.svg4230.png")
Vitamin K antagonists (VKA) are a group of substances that reduce blood clotting by reducing the action of vitamin K. They are used as anticoagulant medications in the prevention of thrombosis, and in pest control, as rodenticides.