Coumadin® (warfarin sodium) is a prescription anticoagulant medication used to treat or prevent blood clots. People taking this drug must follow certain dietary restrictions, as many foods and beverages interact with Coumadin. Foods that are high in vitamin K, for example, can cause problems.
If a person taking Coumadin consumes much more vitamin K than he or she usually does, this will make the drug less effective, which could increase the risk of blood clots. Similarly, if he or she consumes less vitamin K, this could increase the effects of the drug, perhaps even causing a Coumadin overdose. However, you do not need to completely cut out all foods high in vitamin K; you simply need to try to keep your vitamin K intake fairly consistent.
There are a few other Coumadin food interactions that do not appear to be related to vitamin K. The prescribing information for the medication warns that people should avoid cranberry juice or other cranberry products, although there is considerable controversy about the significance of this interaction.
(Click Coumadin Diet to learn more about possible foods to avoid while taking Coumadin and for information on other non-vitamin K food interactions.)