How often can you take Zofran 4 mg for nausea?

Zofran (ondansetron) prevents nausea and vomiting from surgery, chemotherapy, and radiation. It is also used off-label for pregnancy-related nausea, migraines, and vertigo. It blocks serotonin signals in the gut to the brain’s vomiting center. Forms include tablets, ODTs, solution, and injection.

The maximum adult daily dose is 24 mg. Dosing varies by indication:

Mild to moderate chemotherapy-induced nausea

• Adults and children ≥ 12 years: 8 mg 30 minutes before treatment, repeat 8 hours later, then 8 mg every 12 hours for 1–2 days
• Children 4–11 years: 4 mg 30 minutes before treatment, repeat at 4 and 8 hours, then 4 mg every 8 hours for 1–2 days

Children < 4 years: dose determined by provider.

Severe chemotherapy-induced nausea

• Adults and children ≥ 12 years: single 24 mg dose 30 minutes before treatment
• Children < 12 years: dose determined by provider

Radiation-induced nausea

• Total body radiation: 8 mg once daily, 1–2 hours before treatment
• Single high-dose to stomach: 8 mg 1–2 hours before, then 8 mg every 8 hours for 1–2 days
• Daily stomach radiation: 8 mg 1–2 hours before each session, then 8 mg every 8 hours for the day

Children < 18 years: dose determined by provider.

Postoperative nausea

• Adults: 16 mg 1 hour before anesthesia
• Children < 18 years: dose determined by provider

Missed dose

Take as soon as remembered unless near the next dose; then skip and resume schedule. If vomiting, take the missed dose immediately.

Common side effects

• Headache
• Lightheadedness
• Drowsiness
• Constipation
• Diarrhea
• Fatigue

Serious side effects

• Allergic reaction (hives, swelling, breathing difficulty)
• Blurred or temporary vision loss
• Increased risk of heart rhythm problems
• Serotonin syndrome (when combined with other serotonergic drugs): agitation, rapid heart rate, fever, tremor, seizures
• Abnormal heart rhythm (QT prolongation): chest pain, dizziness, fainting, especially with electrolyte imbalances
• Masked signs of bowel obstruction after surgery or chemotherapy
• Risk in phenylketonuria with ODTs (contains aspartame)

Warnings and precautions

• Avoid if allergic to ondansetron or other 5-HT3 antagonists
• Do not combine with apomorphine (risk of severe hypotension)
• Discuss history of long QT syndrome, heart failure, slow heart rate, liver disease, or digestive blockage
• Review all prescription, OTC medications, and supplements for interactions

Sources

• Ondansetron (Rx). Medscape. Accessed June 26, 2025.
• Griddine A, Bush JS. Ondansetron. StatPearls. Updated Feb 15, 2023. Accessed June 26, 2025.