For about 12 percent of the world’s population living with the bowel movement disorder, irritable bowel syndrome, abdominal pain is a part of everyday life. While there are drugs available to treat symptoms like constipation and diarrhea, there is one complication that few irritable bowel syndrome drugs treat effectively. “What’s common to all irritable bowel syndrome patients is the presence of abdominal pain, and it is probably the aspect of the condition that is most difficult to treat,” said Dr. Preston Klassen, Head of Research and Development and Chief Medical Officer at Arena Pharmaceuticals.