You can usually take Zofran every 6 or 12 hours. The frequency depends on other medications you may have. Your health and treatment also affect how much you can take.
Medically reviewed by Alyssa Peckham, PharmD, BCPP
Zofran is a medication known as a serotonin (5-HT3) antagonist. It’s the branded form of ondansetron. It prevents vomiting and nausea. Zofran has Food and Drug Administration (FDA) approval for use in chemotherapy, radiation therapy, and after surgery. Some doctors also prescribe it off-label for pregnancy vomiting and nausea (morning sickness).
You can take Zofran every 6 or 12 hours during treatment, but it depends on why you’re taking the drug and any other prescriptions you might have.
How often can I take it?
The Good Brigade/Getty Images
You should only take Zofran according to a doctor’s prescription. How often you can take it depends on the dosage and type. In general, doctors recommend:
Zofran oral: Initial dose 30 minutes before chemotherapy, 1 hour before surgery, or 1–2 hours before radiation therapy begins. After the initial dose, you might take the medication 1–3 times daily during chemotherapy or radiation therapy and possibly for 1–2 days after treatment finishes.
Zofran injectable: The initial dose is 30 minutes before chemotherapy or immediately before surgery. A healthcare professional might provide additional doses 4 and 8 hours after the first dose if you still have nausea.
Injectable forms of Zofran are intravenous (in the vein) or intramuscular (in the muscle). A healthcare professional will give you these forms of Zofran.
100% online care
Treatment plans in 15 minutes or less for 40+ conditions.
Your dosage also depends on why you’re taking Zofran.
The table below provides a guideline. A doctor might recommend Zofran along with other prescription medications, so it’s important to follow your individual dosing instructions.
Typical Zofran dosage
For surgery
To prevent nausea and vomiting after surgery: • 8 milligrams (mg) every 12 hours (oral) • 4 mg every 12 hours (IV)
During chemotherapy
Some doctors recommend 8 mg every 6 hours of Zofran. The protocol might also involve alternating Zofran with other anti-nausea medications, so you take one of either drug every 3 hours.
Before taking oral Zofran, a doctor might recommend waiting 24–36 hours after your treatment if your chemotherapy IV contains certain drugs like palonosetron (Aloxi).
During pregnancy
Zofran is not a first-line treatment for nausea and vomiting in pregnancy (morning sickness). But if other drugs don’t work, a doctor might recommend 4 mg every 8 hours orally.
The maximum daily dose of Zofran for an adult is 16 mg via IV or 24 mg orally. If you have any liver problems, the maximum dose is 8 mg.
The FDA has not reviewed dosing for children, but doctors usually calculate it at 0.15 mg per kilogram of body weight. This may fall between 12 and 16 mg daily, depending on whether it’s in oral or injectable form.
Possible risks
Oral Zofran comes with possible side effects, including:
headaches
diarrhea
fatigue
dry mouth
Injectable Zofran can cause these same side effects, alongside itching or skin reactions at the injection site.
Taking too much Zofran can lead to an overdose. Signs of overdose are:
sudden blindness or loss of vision for about 2–3 minutes
dizziness or lightheadedness
fainting
irregular heartbeat
constipation
Zofran is not suitable if you also take apomorphine (Apokyn). You should also take caution if you have phenylketonuria (PKU), as one of the components of Zofran can lead to brain damage if you have this condition.
There have been several studies about the effects of Zofran on pregnancy. Research has so far found no connection with pregnancy issues and pregnancy loss.
However, a paper from 2018 that looked at data from two large studies found a possible association between Zofran and an increased risk of cleft palate defects or issues in fetal kidney development. The study authors said the association might be the result of chance.
Additionally, a large 2023 systematic review noted that more research was necessary to understand the risks and benefits of Zofran use during pregnancy.
The American College of Obstetricians and Gynecologists recommends treating pregnancy nausea and vomiting with pyridoxine (vitamin B6) or doxylamine (Unisom). If these don’t work, Zofran might be an alternative.
Free prescription coupons
Seriously … free. Explore prices that beat the competition 70% of the time.
If you’re having chemotherapy and experiencing nausea and vomiting, alternatives to Zofran might include other serotonin antagonists or drugs of different classes, like NK-1 receptor agonists and dopamine agonists.
A doctor might recommend anti-nausea drugs alone or in combination with other medications not on this list.
If you need help covering the cost of medications, the free Optum Perks Discount Card could help you save up to 80% on prescription drugs. Follow the links on drug names for savings on that medication, or search for a specific drug here.
Summary
Zofran is FDA-approved for nausea and vomiting after surgery or during chemotherapy and radiation to treat cancer.
Depending on a doctor’s recommendation, you can take Zofran every 6 to 12 hours. If Zofran doesn’t work or if you can’t take the drug for any reason, alternatives might include other serotonin antagonists, a dopamine antagonist, or an NK-1 receptor antagonist.
Parker SE, et al. (2018). Ondansetron for treatment of nausea and vomiting of pregnancy and the risk of specific birth defects. https://pubmed.ncbi.nlm.nih.gov/29995744/
