Ondansetron is a widely used antiemetic medication that effectively prevents nausea and vomiting from various causes, including chemotherapy, radiation therapy, surgery, and off-label for pregnancy-related symptoms. As a selective 5-HT3 serotonin receptor antagonist, it works by blocking serotonin action both centrally in the brain's chemoreceptor trigger zone and peripherally in the gut, providing reliable relief across these etiologies.