There is a lot of evidence that proves serotonin (5-HT), modulated via 5-HT3 and 5-HT4 receptors, plays a significant role in the control of gastrointestinal secretion, sensation, perception of visceral stimulation at peripheral and central locations, and motility. Dysfunction in these receptors can lead to intestinal and extraintestinal symptoms in IBS, such as constipation or diarrhea. Here, HTR3A is linked to irritable bowel syndrome.