Ondansetron is used alone or with other medications to prevent nausea and vomiting caused by cancer drug treatment (chemotherapy), radiation treatment, or drugs used to put you to sleep before surgery. Ondansetron works by blocking one of the body’s natural substances (serotonin) that causes vomiting.

Some common side effects of ondansetron are headache, malaise/fatigue, constipation, poor oxygenation, drowsiness, diarrhea, dizziness, fever, gynecologic disorder, anxiety, urinary retention, severe itching, injection-site pain, numbness and tingling, cold sensation, and elevated liver function test results.