It is a serotonin 5-HT3 receptor antagonist used mainly as an antiemetic (to treat nausea
and vomiting), often following
chemotherapy. Its effects are thought to be on both peripheral
and central nerves. Ondansetron reduces the activity of the vagus nerve, which deactivates the vomiting center in the medulla oblongata, and also blocks serotonin receptors in the chemoreceptor trigger zone.