Ondansetron is known to be a highly selective 5-HT3 receptor antagonist. 5HT3 is a substance released during chemotherapy or radiation therapy, this substance is present in the small intestine and causes the vomiting reflex.

Ondansetron is one of the most commonly used 5-HT3 receptor antagonists. The drug can be used alone or in combination with other drugs to help improve symptoms such as nausea and vomiting in patients after surgery or undergoing chemotherapy, radiation treatment for cancer.