Q. A 68-year-old man with a history of atrial fibrillation presents to the clinic complaining of easy bruising and prolonged bleeding from minor cuts over the past few weeks. He has been on warfarin for several years. Recently, he started taking over-the-counter supplements recommended by a friend for boosting memory and cognitive function. On further inquiry, it is revealed that these supplements are rich in various vitamins and minerals. His INR is higher than the therapeutic range. Which condition is this patient likely suffering from?