You can eat prunes while taking Coumadin. Coumadin is a blood-thinner, and large amounts of vitamin K can decrease its effect.  Prunes are not particularly high in Vitamin K.  For instance, 6 prunes have 30 mcg, while collard greens, a high-vitamin K food, has over 800 mcg per cup.  It is important to have a consistent intake of vitamin K from day-to-day so your doctor can regulate your Coumadin dose around it.