Ask the doctor: Warfarin interactions
Q. There is a long list of drugs and substances that interact with Coumadin (warfarin). Does this mean they make Coumadin more effective, or less effective?
A. This is an important and useful question. Some medications can strengthen warfarin's anti-clotting effect, while others can weaken it. There are really two ways in which other drugs influence the effectiveness of warfarin.