Irritable bowel syndrome (IBS) is a functional gastrointestinal (GI) disorder, meaning that the symptoms are caused by changes in how the GI tract works. Food is digested, or broken down, in the GI tract. IBS is not a disease. Symptoms can come and go repeatedly without signs of damage to the GI tract. The most common symptoms of IBS are abdominal pain or discomfort, often reported as cramping, along with diarrhea, constipation, or both. This publication by the National Institutes of Health (Publication No. 12-4686) discusses IBS, symptoms, causes, diagnosis, and treatments.