n. a serotonin antagonist at the 5-HT3 serotonin receptor that is used for the prevention and treatment of nausea resulting from chemotherapy or anesthesia. When combined with appropriate behavior therapy, it may also be an effective adjunctive agent in managing certain types of alcoholism, although it is not officially approved by the U.S. Food and Drug Administration for such treatment. U.S. trade name: Zofran.