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Zofran: 7 things you should know

Medically reviewed by Carmen Fookes, BPharm. Last updated on Nov 13, 2018.

1. How it works

  • Zofran is a brand (trade) name for ondansetron. Ondansetron treats and prevents nausea and vomiting by an unknown mechanism, possibly by a direct effect on the CTZ (the area of the brain associated with vomiting), the vagus nerve or both. The neurotransmitter, serotonin, appears to play a role in ondansetron's effect.
  • 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.
  • Effective at preventing postoperative nausea and vomiting.
  • Zofran is available as tablets, orally disintegrating tablets, and a solution.
  • 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:

  • Tiredness, a headache, drowsiness, dizziness, constipation, flushing, itching, slowed heart rate, raised body temperature, and diarrhea.
  • Rarely may cause hiccups, blurred vision or vision loss, a rash or liver disturbances, or affect the heartbeat (more likely at higher dosages).
  • May mask a progressive ileus or gastric distension. Monitor for decreased bowel activity.
  • Interaction or overdosage may cause serotonin syndrome (symptoms include agitation, hallucinations, fast heart rate, dizziness, muscle tremor, nausea, vomiting, diarrhea).
  • May interact with some medications including apomorphine (may cause a profound drop in blood pressure and loss of consciousness), and drugs metabolized by CYP3A4 (although few clinically significant interactions have been reported).
  • 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.
  • Orally disintegrating Zofran tablets may contain phenylalanine. Tell your doctor if you have phenylketonuria (PKU).

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 relieves and prevents nausea and vomiting. Side effects may include constipation and headache.

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, delirium]), fast heart rate, dizziness, flushing, muscle tremor or rigidity and stomach symptoms [including nausea, vomiting, diarrhea]).
  • Report to your doctor any other unusual side effects.
  • If Zofran makes you dizzy or drowsy, do not drive or operate machinery while affected and avoid alcohol.

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.

7. Interactions

Medicines that interact with Zofran may either decrease its effect, affect how long it works for, 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.


Zofran (ondansetron). Revised 10/2019. GlaxoSmithKline LLC

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.

Copyright 1996-2021 Revision date: November 5, 2019.

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