Hi Char: I have had IBS for about 35 years. Then, I was found to have osteopinia (SP?) so they put me on fosomax. I have absolutely no side effects with fosomax. I also take 1500 mg of calcium per day with no more than 400 IU of vitamin D. My last bone density test was normal. I don't think IBS is related to osteoporosis, or vice versa. I have broken a lot of bones (sports) and supposedly the body uses up calcium to heal bones, thus the less dense bones. Also, my family has a history of osteoporosis. I have really bad IBS, and if the fosomax in any way made it worse, I'd know. In fact, the calcium and fosomax seem to help the IBS, if anything. Hope this helps!