Alosetron (GR 68755) is a Serotonin 5HT3-receptor antagonist that is used in treatment of irritable bowel syndrome. IC50 Value: Target: 5-HT Receptor Alosetron has an antagonist action on the 5-HT3 receptors of the enteric nervous system of the gastrointestinal tract. While being a 5-HT3 antagonist like ondansetron, it is not classified or approved as an antiemetic. Since stimulation of 5-HT3 receptors is positively correlated with gastrointestinal motility, alosetron's 5-HT3 antagonism slows the movement of fecal matter through the large intestine, increasing the extent to which water is absorbed, and decreasing the moisture and volume of the remaining waste products. From Wikipedia.