... Warfarin (thin blood) but they are not the same. Warfarin is generic so the FDA allows for generic dosage variance to be +/_ 5% off . So that's is why patients INR fluctuate a lot when they are on Warfarin. Some people are allergic to warfarin and that is why they can not reach a therapeutic dose. My husband was on warfarin and we were told about this, "FDA 5% +/ variance dosage on generic drugs" and after 3 months of being tortured we requested to placed on Coumadin. Guess what? He had been on 4 mg daily since 2013 with an INR 2.1-2.4 and has never had to change his dose. Another reason why people are sensitive to Warfarin is because they might have Lupus Coagulopathy. FYI