Viberzi Overview. Viberzi is a prescription medication used to irritable bowel syndrome with diarrhea (IBS-D) in adults. Viberzi belongs to a group of drugs called mu-opioid receptor antaognists. The exact mechanism of Viberzi in IBS-D is not known, but Viberzi interacts with opioid receptors in the gut. This medication comes in tablet form and is taken 2 times a day with food.