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.