Yes clots can form even if you're on coumadin. I've been on coumadin for 16 years now due to an aortic valve being replaced 16 years ago and have been hospitalized on 3 separate occasions during those 16 years with blood clots. This is why at least monthly pro-times are important. You should be within a therapeutic INR level that is determined by your physician. If you fall short of that range you have a risk of blood clots. If you fall above that range you run the risk of bleeding. Monitoring your INR is crucial in managing your disease. Certain foods and dietary supplements will effect your INR as will changes in medication and over the counter medications. If you're changing your diet radically or adding new meds whether over the counter or prescript
ions it is necessary to have more frequent pro times. Good luck.