Which of the following interactions is known to enhance the effect of warfarin?

Cranberry juice is known to enhance the effect of warfarin, primarily due to its potential to inhibit certain liver enzymes involved in drug metabolism, particularly CYP2C9, which is responsible for metabolizing warfarin. By inhibiting this enzyme, cranberry juice can increase the levels of warfarin in the bloodstream, leading to an increased anticoagulant effect. This interaction may increase the risk of bleeding and necessitate careful monitoring of INR levels for patients consuming cranberry juice while on warfarin therapy.

On the other hand, antacid medications generally do not have a significant impact on warfarin's anticoagulant effect and are not known to cause interactions that enhance its effect. St. John's Wort is more commonly associated with reducing the effectiveness of warfarin due to its induction of various cytochrome P450 enzymes, which can lead to decreased warfarin levels. Over-the-counter pain medications vary widely in mechanism but do not have a well-established interaction that enhances the effects of warfarin like cranberry juice does.