What could be causing my coumadin (warfarin) levels to go up and down continually?

Diet or generic...: Dietary foods can make Coumadin levels go up and down, so can certain medications. If all else is the same, the biggest cause is getting generic Coumadin (warfarin). The fda allows generic houses to be +/- 20% bio-equivalent of their trade name partners, so a dose could theoretically be off by as much by 40%. Ask your doctor to try trade name coumadin, be careful with a drug with a narrow range.