dicoumarol

(dicumarol, bis-hydroxycoumarin, 3,3'-methylene-bis(4-hydroxycoumarin))

A naturally occurring anticoagulant that acts as a vitamin K antagonist, similar to warfarin, by depleting stored vitamin K.

Coumarin is metabolized by fungi into 4-hydroxycoumarin and then dicoumarol.
Coumarin is a bitter-tasting but sweet-smelling substance made by plants that does not itself affect coagulation, but which is transformed in mouldy feeds or silages by a number of species of fungi, into this that affects coagulation.
It was discovered in mouldy wet sweet-clover hay, as the cause of a naturally occurring bleeding disease in cattle.

While its high doses can result in uncontrolled bleeding, it has been utilized for preventing and treating thrombosis (formation of a blood clot) (e.g. deep vein thrombosis), thrombophlebitis (inflammation of a vein), and embolism (a blocked artery), sometimes in post-operational periods, and other blood clotting disorders.