Skip to main content

Zofran: 7 things you should know

Medically reviewed by Carmen Pope, BPharm. Last updated on April 4, 2023.

1. How it works

  • Zofran is a brand (trade) name for ondansetron which may be used to treat or prevent nausea and vomiting.
  • Experts aren't sure exactly how Zofran (ondansetron) works and if its antiemetic action is mediated by a direct effect on the CTZ (the area of the brain associated with vomiting), the vagus nerve, or both. Zofran is a selective 5‑HT3 receptor antagonist and the neurotransmitter, serotonin, appears to play a role in ondansetron's effect. Cytotoxic chemotherapy appears to be associated with the release of serotonin from the enterochromaffin cells of the small intestine and the released serotonin may stimulate the vagal afferents through the 5‑HT3 receptors and initiate the vomiting reflex. Zofran is not a dopamine‑receptor antagonist.
  • Zofran belongs to the class of medicines known as 5-HT3 receptor antagonists.

2. Upsides

  • Effective for the prevention of nausea and vomiting associated with cancer chemotherapy, including highly emetogenic (a high probability of causing vomiting) chemotherapy.
  • May also be used to prevent nausea and vomiting associated with radiotherapy - this includes total body irradiation or single or multiple high-dose or daily fractions to the abdomen. The usual dosage is 8mg administered one to two hours before radiotherapy with doses every 8 hours thereafter depending on the type of radiotherapy.
  • Effective at preventing postoperative nausea and vomiting. The usual dosage is 16mg administered 1 hour before the induction of anesthesia.
  • Zofran is available as tablets, orally disintegrating tablets, and an oral solution. Tablets and orally disintegrating tablets are available in 4mg and 8mg strengths. Zofran oral solution is 4mg/5mL with a strawberry odor.
  • For highly emetogenic cancer chemotherapy a single 24mg dose administered 30 minutes before the start of a single-day highly emetogenic chemotherapy (such as cisplatin) has a good effect. For moderately emetogenic chemotherapy, an 8mg dose is administered 30 minutes before the start of chemotherapy with a subsequent 8mg dose administered 8 hours after the first dose. Then administer twice a day for 1 to 2 days after completion of the chemotherapy.
  • May be given to children aged 4 and older. The usual starting dose is 4mg for those aged 4 to 11 years of age or 8mg for those aged 12 to 17 years of age.
  • Zofran is available as a generic under the name ondansetron.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • A headache, hypoxia (low oxygen), fever, dizziness, gynecological disorders, anxiety or agitation, urinary retention, and itching are the most common side effects reported.
  • Rarely may cause hiccups, flushing, blurred vision or vision loss, a rash or liver disturbances, or affect the heartbeat (more likely at higher dosages). Allergic reactions have also been reported.
  • May mask a progressive ileus or gastric distension. Monitor for decreased bowel activity.
  • May interact with some medications including apomorphine (which may cause a profound drop in blood pressure and loss of consciousness), drugs metabolized by CYP3A4 (although few clinically significant interactions have been reported), or other medications that also release serotonin.
  • May not be suitable for some people including those with liver disease, a personal or family history of long QT syndrome (a heart rhythm disorder), or a previous reaction to other selective 5-HT3 receptor antagonists. Do not exceed a total daily dose of 8mg in those with severe hepatic impairment.
  • Orally disintegrating Zofran tablets may contain phenylalanine. Tell your doctor if you have phenylketonuria (PKU).
  • Serotonin syndrome has been reported with 5-HT3 receptor antagonists, such as Zofran, particularly if used in combination with other medications that also release serotonin such as lithium, or fentanyl. Some cases have been fatal. Symptoms include mental status changes such as agitation, hallucinations, coma, or delirium; a fast heart rate; dizziness; flushing; muscle tremor or rigidity; and stomach symptoms (including nausea, vomiting, and diarrhea).
  • There is not enough data to recommend the use of Zofran during pregnancy. A case-control study reported an association between ondansetron use and cleft palate; however, this could have been a chance finding. It is not known if Zofran is passed into breast milk.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

  • Zofran may be used for the treatment and prevention of nausea and vomiting caused by cancer chemotherapy, radiation, or surgery. It is approved for use in adults and children over the age of 4. A headache, hypoxia, and fever are some of the more commonly reported side effects.

5. Tips

  • Take as directed. May be taken with or without food.
  • When used to prevent nausea associated with chemotherapy, Zofran is usually taken 30 minutes before chemotherapy. When used to prevent nausea associated with radiotherapy, Zofran is usually taken one-to-two hours before radiotherapy. When used to prevent nausea associated with surgery, Zofran is usually taken one hour before anesthesia.
  • The dose of Zofran orally disintegrating tablets is the same as Zofran solution.
  • When taking the orally disintegrating tablets, peel back the foil (do not attempt to push the tablet through the foil). Allow the tablet to dissolve in your mouth without chewing.
  • When taking Zofran oral solution, measure the correct dosage with the dosing syringe provided.
  • Consider laxatives to relieve or prevent constipation associated with Zofran.
  • Monitor for serotonin syndrome (symptoms include mental status changes [such as agitation, hallucinations, coma, and delirium]), fast heart rate, dizziness, flushing, muscle tremor or rigidity, and stomach symptoms [including nausea, vomiting, or diarrhea]).
  • Report to your doctor any other unusual side effects, such as a change in your heart rate, feeling lightheaded (especially when going from a sitting to a standing position), or if you develop any signs of an allergic reaction.
  • If Zofran makes you dizzy or drowsy, do not drive or operate machinery while affected, and avoid alcohol.
  • Tell your doctor or other health care provider about all the medicines you take, including prescription and over-the-counter (OTC) medicines, vitamins, and herbal supplements. Let them know if you eat grapefruit or drink grapefruit juice. Zofran interacts with several medicines and it may not be safe to take them together.
  • Tell your doctor if you are pregnant or intend to become pregnant. It is not known how Zofran affects the unborn child. It is not known if Zofran is safe during breastfeeding.

6. Response and effectiveness

  • The peak effect of Zofran is reached within 1.5-2 hours. The onset of effect is faster with the orally disintegrating or liquid form.
  • In one trial of patients receiving highly emetogenic cancer chemotherapy, 66% of patients received ondansetron 24mg as a single dose, 55% of patients received ondansetron 8mg every 8 hours for two doses, and 55% received ondansetron 32mg once a day. All completed the 24-hour trial period with zero emetic episodes and no rescue antiemetics.
  • For other indications, such as postoperative nausea and vomiting, Zofran was significantly more effective than a placebo (an inactive medicine).

7. Interactions

Medicines that interact with Zofran may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with Zofran. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with Zofran include:

  • antibiotics, such as clarithromycin or erythromycin
  • antidepressants, such as tricyclic antidepressants (eg, amitriptyline), monoamine oxidase inhibitors (eg, isocarboxazid, phenelzine, and tranylcypromine), venlafaxine, and SSRIs (eg, paroxetine, sertraline)
  • anticonvulsants, such as phenytoin, phenobarbital, or primidone
  • antipsychotics (such as butyrophenones, phenothiazines, or thioxanthenes) and atypical antipsychotics (eg, olanzapine, quetiapine, ziprasidone)
  • beta-blockers, such as atenolol or bisoprolol
  • lithium
  • medications that correct an irregular heartbeat, such as amiodarone or disopyramide
  • medications that induce or inhibit CYP2D6, CYP3A4, or CYP1A2 enzymes
  • opioids, such as oxycodone or morphine
  • other medications that affect serotonin, such as amphetamines, fentanyl, tramadol, triptans (eg, almotriptan, eletriptan, or sumatriptan), or St. John's Wort.

Note that this list is not all-inclusive and includes only common medications that may interact with Zofran. You should refer to the prescribing information for Zofran for a complete list of interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Zofran only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2023 Revision date: April 4, 2023.