Ondansetron, marketed under the brand name Zofran, is a medication used to prevent nausea and vomiting caused by cancer chemotherapy, radiation therapy, or surgery. It is also effective for treating gastroenteritis. It has no effect on vomiting caused by motion sickness. It can be given by mouth or by injection into a muscle or into a vein.
Common side effects include diarrhea, constipation, headache, sleepiness, and itchiness. Serious side effects include QT prolongation and severe allergic reaction. It appears to be safe during pregnancy but has not been well studied in this group. It is a serotonin 5-HT3 receptor antagonist. It does not have any effect on dopamine receptors or muscarinic receptors.
Ondansetron was patented in 1984 and approved for medical use in 1990. It is on the World Health Organization's List of Essential Medicines, the safest and most effective medicines needed in a health system. It is available as a generic medication. The wholesale cost of the injectable form in the developing world is about US$0.10 to US$0.76 per dose. In the United States it costs about US$1.37 per tablet. In 2016 it was the 91st most prescribed medication in the United States with more than 8 million prescriptions.
Although an effective antiemetic agent, the high cost of brand-name ondansetron initially limited its use to controlling postoperative nausea and vomiting and chemotherapy-induced nausea and vomiting.
A number of medications including ondansetron appear to be effective in controlling postoperative nausea and vomiting. It is more effective than metoclopramide, and less sedating than cyclizine or droperidol.