Ondansetron is a medication primarily used to prevent nausea and vomiting caused by chemotherapy, radiation therapy, or surgery. It works as a selective serotonin 5-HT3 receptor antagonist, blocking the action of serotonin in the brain and gastrointestinal tract. Ondansetron is available in various forms, including oral tablets, dissolvable films, and intravenous injections. It is commonly prescribed due to its effectiveness in managing acute nausea and vomiting.