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Ondansetron

Medication 5-HT3 antiemetic digestive
Aka: Zofran
Brands seen in Singapore: Zofran, Odnatron, Ondavell, Natzo, Vomiz
Not medical advice. Check with your doctor or pharmacist before you start, stop or change the timing of anything you take.
How to use
What it’s for
Prescribed to prevent or treat nausea and vomiting
When to take
HealthHub: usually as needed; regularly only if directed
Take with
HealthHub: with or without food
Pros & cons
Pros
  • HealthHub: blocks the serotonin signal behind nausea
  • FDA label: used before chemo, radiotherapy and surgery
  • SG register: 4 mg and 8 mg tablets, plus injections
Cons
  • HealthHub: constipation, headache and drowsiness
  • FDA label: it can prolong the qt interval
  • HealthHub: rarely, serotonin syndrome can occur
Sources
  1. HSA — Listing of Registered Therapeutic Products (data.gov.sg open dataset, 5,511 rows, cached in full and filtered locally) · read 2026-08-27
    what it says
    “All 17 registered ondansetron products carry Forensicclassification 'Prescription Only', ATC A04AA01 — SIN05133P ZOFRAN TABLET 8 mg · SIN13714P ODNATRON · SIN15004P ONDAVELL · SIN15423P NATZO · SIN17125P VOMIZ, plus injections.”
  2. HealthHub (Pharmaceutical Society of Singapore) — Ondansetron: what is this medication for · read 2026-08-27
    what it says
    “Ondansetron is used to prevent or treat nausea and vomiting. Ondansetron works by blocking the actions of a chemical called serotonin that causes nausea and vomiting.”
  3. HealthHub — Ondansetron: how should I take or use this medication · read 2026-08-27
    what it says
    “You may take Ondansetron with or without food.”
  4. HealthHub — Ondansetron: missed dose · read 2026-08-27
    what it says
    “Ondansetron is generally taken on an as-needed basis. Take them regularly only when directed by the doctor. If you forget to take a dose, take it as soon as you remember.”
  5. HealthHub — Ondansetron: precautions · read 2026-08-27
    what it says
    “You have a history of: Liver condition; Abnormal heart rhythm; Recent surgery in the stomach area. You are pregnant or breastfeeding. You are taking any other medications, including supplements, traditional medications and herbal remedies.”
  6. HealthHub — Ondansetron: common side effects · read 2026-08-27
    what it says
    “Constipation … Diarrhea … Headache … Drowsiness. Avoid driving or engaging in activities that require concentration … Anxiety”
  7. HealthHub — Ondansetron: rare but serious side effects · read 2026-08-27
    what it says
    “Ondansetron is generally safe, but very rarely a serious condition known as Serotonin syndrome may occur. This can cause serious health problems that may sometimes be life threatening.”
  8. HealthHub — Ondansetron: what food or medication should I avoid · read 2026-08-27
    what it says
    “Certain heart medications (e.g. Amiodarone, Sotalol); Domperidone which is used for treating nausea and vomiting; Apomorphine, which is used for treating Parkinson's disease”
  9. US label for ondansetron tablets, section 2 Dosage and Administration, via openFDA drug/label.json (effective 2024-04-24) · read 2026-08-27
    what it says
    “A single 24 mg dose administered 30 minutes before the start of single-day highly emetogenic chemotherapy … Postoperative 16 mg administered 1 hour before induction of anesthesia … do not exceed a total daily dose of 8 mg”
  10. US label for ondansetron tablets, section 1 Indications and Usage, via openFDA · read 2026-08-27
    what it says
    “indicated for the prevention of nausea and vomiting associated with: highly emetogenic cancer chemotherapy … moderately emetogenic cancer chemotherapy … radiotherapy … Ondansetron tablets are also indicated for the prevention of postoperative nausea and/or vomiting.”
  11. US label for ondansetron tablets, section 4 Contraindications, via openFDA · read 2026-08-27
    what it says
    “Ondansetron is contraindicated in patients: … receiving concomitant apomorphine due to the risk of profound hypotension and loss of consciousness”
  12. US label for ondansetron tablets, section 5 Warnings and Precautions, via openFDA · read 2026-08-27
    what it says
    “QT Interval Prolongation and Torsade de Pointes: Avoid ondansetron tablets in patients with congenital long QT syndrome; monitor with electrocardiograms (ECGs) if concomitant electrolyte abnormalities, cardiac failure or arrhythmias, or use of other QT prolonging drugs.”
  13. US label for ondansetron tablets, section 7 Drug Interactions, via openFDA · read 2026-08-27
    what it says
    “Serotonin syndrome … has been described following the concomitant use of 5-HT3 receptor antagonists and other serotonergic drugs, including SSRIs and SNRIs … potent inducers of CYP3A4 (i.e., phenytoin, carbamazepine, and rifampin)”
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Updated 2026-08-29. Every line above traces to a numbered source. Kozen-X is not a medical device and does not give medical advice. It lists what published sources have written down — nothing more. A pair not listed is unrecorded, not cleared. Before you start, stop or re-time anything, talk to your doctor or pharmacist.