The article presents a study exploring the interaction of over-the-counter (OTC) drug noscapine and acenocoumarol and phenprocoumon. Topics discussed include information on the anticoagulant effects of the drugs by inhibiting the synthesis of vitamin K–dependent clotting factors; determining the nature of the drug interaction between noscapine and warfarin; and the information on the interaction between vitamin K antagonists and noscapine resulting in increased international normalized ratio.