Warfarin is the most commonly prescribed blood thinner and is used to prevent clotting and resulting embolisms. Ironically, it was first developed as a rodent poison (causing massive internal bleeding when it is ingested), but since the 1950s has been used as a pharmaceutical (ironically, after someone attempting to consume rat poison in a suicide attempt survived it). It was first developed after animals died of internal bleeding after consuming mouldy hay, but the active ingredient was not identified until several years later. Warfarin works by preventing chemical reduction of Vitamin K