Ondansetron is an antiemetic medication, which means it’s used to prevent nausea and vomiting. It works by blocking the action of a chemical messenger known as serotonin in the brain and the gut.

It is a serotonin 5-HT3 receptor antagonist ("setron") which inhibits serotonin binding to the 5-HT3 receptors 
  1. in the terminals of afferent fibres of the vagus nerve. This inhibits the activation of the vomiting center in the medulla oblongata.
  2. and in the CTZ of Medulla oblongata of brain. 


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