Ondansetron (Zofran): What It Does and What You Need to Know

Ever had nausea that won't quit after surgery or chemotherapy? Ondansetron — often known by the brand Zofran — is a go-to medicine doctors use to stop severe nausea and vomiting. It works fast for many people, comes as a tablet, dissolving wafer, and IV, and is usually given when other remedies aren’t enough.

How ondansetron works and common uses

Ondansetron blocks serotonin signals in certain gut and brain receptors (5-HT3 receptors) that trigger nausea. That makes it especially useful for nausea from chemotherapy, radiation, and after surgery. Doctors may also use it for severe stomach flu or other causes of persistent vomiting. It’s not a cure for the underlying cause — it just controls the symptom so you can keep fluids down and feel better.

Formulations: oral tablet, orally disintegrating tablet (ODT), and intravenous (IV). ODTs are handy if you’re too nauseous to swallow. IV is common in hospitals after surgery or during chemo sessions.

Practical dosing tips and what to expect

Typical adult doses vary by situation: for postoperative nausea, a single 4 mg dose is common; for chemo-related nausea, higher or repeated doses may be used. Children get weight-based dosing. Always follow your prescriber’s instructions — exact timing and dose depend on why you need it.

Take oral ondansetron with or without food. If you use the dissolving tablet, let it dissolve on your tongue; don’t chew. If you miss a dose, take it when you remember unless the next dose is near — don’t double up.

Safety, side effects, and interactions

Most people tolerate ondansetron well. Common side effects are headache, constipation, and fatigue. A rare but important risk is QT prolongation — a heart rhythm change — which can be dangerous when combined with other QT‑extending drugs or in people with low potassium/magnesium or certain heart problems. Tell your doctor about other medicines you take: many antidepressants, some antibiotics, and certain antifungals can interact.

There’s also a small risk of serotonin syndrome if ondansetron is combined with other serotonin-active drugs (SSRIs, SNRIs, triptans, MAOIs). Watch for agitation, rapid heart rate, high body temperature, or severe coordination problems and get medical help if they occur.

Pregnancy note: ondansetron is commonly used for severe pregnancy nausea, but some studies raised questions about rare birth-defect risks. Talk with your OB/GYN to weigh benefits and risks for your case.

Storage and safety: store at room temperature, keep away from kids, and check expiry dates. Ondansetron requires a prescription — don’t buy from unverified sources. If you suspect overdose (extreme drowsiness, fainting, chest pain, or seizures), seek emergency care immediately.

If you’re unsure whether ondansetron is right for you, ask your doctor or pharmacist. It’s a useful tool against tough nausea, but like any medicine, it works best when matched to your situation and taken safely.