This happens in the presence of naturally occurring formaldehyde, which allows attachment of a second 4-hydroxycoumarin molecule through the linking carbon of the formaldehyde, to the 3-position of the first 4-hydroxycoumarin molecule, to give the semi-dimer the motif of the drug class.

Dicoumarol appears as a fermentation product in spoiled sweet clover silages and is considered a mycotoxin.

[2] After the identification of dicoumarol and its anticoagulant activity, it became the prototype for a class of drugs.

4-Hydroxycoumarin forms the core of the chemical structure of anticoagulants known collectively as 4-hydroxycoumarins.

They include, for example, warfarin, a pharmaceutical drug used to prevent formation of blood clots, and brodifacoum, a widely used rodenticide.