Douglas A. Drossman, MD: Well IBS is diagnosed based on a certain collection of symptoms. Basically these symptoms need to be present for about 6 months, and to fulfill certain criteria for 3 months. And those criteria are abdominal pain or discomfort that's either relieved by a bowel movement or associated with diarrhea or constipation, meaning a looser bowel movement or a harder bowel movement. Two of those three would fulfill the criteria. But in addition to that, you have to eliminate what we call red flags, or certain symptoms or patterns that might suggest another condition. That would mean something like if there's blood in the stool, if there is significant weight loss, if there is a family history of colon cancer or inflammatory bowel disease, if there is an abnormality on an abdominal exam. And if any of those are present, you need to do further studies.