Diphenadione is a vitamin K antagonist that has anticoagulant effects and is used as a rodenticide against rats, mice, voles, ground squirrels and other rodents.

The chemical compound is an anti-coagulant with active half-life longer than warfarin and other synthetic 1,3-indandione anticoagulants.

[3][4] It is toxic to mammals, in all forms; exposure and oral ingestion of the toxin may cause irregular heartbeat and major maladies associated with its impact on blood clotting, depending on dose.

[6]: 436  For purposes of treating toxicity on exposure, diphenadione is grouped with other vitamin K antagonists (coumarins and indandiones); despite being directed at rodents and being judged as less hazardous to humans and domestic animals than other rodenticides in use[when?]

(by the U.S. Environmental Protection Agency), indandione anticoagulants, nevertheless, "may cause human toxicity at a much lower dose than conventional 'first-generation anticoagulants'… and can bioaccumulate in the liver.