A 24-year-old woman is evaluated for a 3-year history of irritable bowel syndrome characterized by daily abdominal pain and infrequent, lumpy, hard-to-pass stools. She has no family history of colorectal cancer or inflammatory bowel disease. She is otherwise healthy and takes no medications. Her symptoms persist despite her FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) avoidance diet, psyllium use, and a trial of polyethylene glycol.
Physical examination is normal.
Which of the following is the most appropriate next step in management?
