Ondansetron tablets are used to prevent and treat nausea and vomiting caused by chemotherapy, radiation therapy, and surgery, as well as in some cases of severe vomiting from gastroenteritis or other illnesses .Main UsesChemotherapy-induced nausea and vomiting (CINV): Ondansetron is commonly given before and after cancer chemotherapy to prevent nausea and vomiting, especially with highly emetogenic (vomit‑causing) drugs .Radiation-induced nausea and vomiting: It is used before and after radiation therapy (especially to the abdomen or whole body) to reduce nausea and vomiting .Postoperative nausea and vomiting (PONV): A single dose is often given before anesthesia to prevent nausea and vomiting after surgery Other causes of nausea/vomiting: Sometimes used off‑label for severe vomiting due to gastroenteritis, food poisoning, or in pregnancy (though not first‑line for morning sickness)