Hi, sometimes its the iron in the vitamin that causes stomache upset. Try another vitamin supplement without iron and see if that helps. There are also vitamins with different iron salts that are less upsetting to your tummy. I would avoid the mega-dose vitamin supplements that you find in health food stores. The body usually doesn't need these high doses. If a doctor is perscribing high dose of a certain supplement(s) for a certain condition than go along with what he prescribes.