coumarin /ko̅o̅″mərin/ , a class of orally active anticoagulant agents with warfarin as its prototype. ▪ INDICATIONS: It is prescribed for prophylaxis and treatment of thrombosis and embolism. ▪ CONTRAINDICATIONS: Known hypersensitivity to the drug prohibits its use. It is not prescribed to patients who are at risk for hemorrhage or who are pregnant. ▪ ADVERSE EFFECTS: The most serious adverse reaction is hemorrhage. Many other drugs interact with this drug to increase or decrease its effect.