ONDANSETRON Alphapharm contains a medicine called ondansetron. This belongs to a group of medicines called Serotonin receptor-3 antagonists. ONDANSETRON Alphapharm is used to help stop the nausea (sick feeling) and vomiting which can occur after medical treatments and operations. ONDANSETRON Alphapharm should only be used to treat the nausea and vomiting for which it has been prescribed.