To prevent nausea from chemotherapy, take this medication by mouth usually within 30 minutes before treatment begins. To prevent nausea from radiation treatment, take this medication by mouth 1 to 2 hours before the start of your treatment. To prevent nausea after surgery, take ondansetron by mouth 1 hour before the start of surgery. This medication may be taken with or without food. However, your doctor may tell you not to eat before chemotherapy, radiation, or surgery.

If you are using the liquid form of this medication, use a special measuring spoon or device to measure out your prescribed dose. Do not use a household spoon because you may not get the correct dose.

Take any other doses as directed by your doctor. Ondansetron may be taken up to 3 times a day for 1 to 2 days after your chemotherapy or radiation treatment is finished. If you are taking this medication on a prescribed schedule, take it regularly in order to get the most benefit from it. To help you remember, take it at the same times each day.

The dosage is based on your medical condition and response to treatment. Children's dosage may also be based on age and weight. Take this medication exactly as directed. Do not take more medication or take it more often than prescribed. Ask your doctor or pharmacist if you have questions.

Tell your doctor if your condition does not get better or if it gets worse.