Zofran (Ondansetron) Side Effects, Important Information, Before Taking, How to Take

Zofran is an antiemetic drug – which means that it is used to block the actions of chemicals (mainly, serotonin) which are produced naturally in the body and cause vomiting. Therefore, it is used to prevent nausea and vomiting caused by surgery, cancer chemotherapy or radiation treatment. It may also be used for gastroenteritis but is not suitable for vomiting caused by motion sickness.




Common side effects include confusion, racing heartbeat, dizziness, light-headedness, fever, headache, shortness of breath, unusual tiredness or weakness and constipation. It is advisable to contact your doctor if these side effects persist or interfere with your everyday life.

Serious side effects include stomach pain, muscle spasm or stiffness, problems in eyesight such as temporary loss of vision or blurred vision, chest pain, severe dizziness, hallucination, disorientation and fainting.

It is highly unlikely that you develop a grave allergic reaction to this drug but if you see signs of an allergy such as rash, itching, swelling and breathing problems, then contact your doctor immediately.



Take this medicine exactly as has been instructed by your healthcare provider.

If you have been prescribed this medicine to treat nausea from chemotherapy, then it is often taken thirty minutes before treatment starts. If it is used for radiation treatment, then it might be taken one to two hours before the treatment and if it is used for surgery, then it is recommended that you take the dose an hour before your surgery.

Your doctor might tell you to continue this medication after chemotherapy as well and it is usually taken three times a day for one to two days after treatment. Do not prolong or shorten the prescribed period by yourself and do not take bigger or smaller doses than recommended.

It can be taken with or without food – but if you have been told not to eat before your treatment, then follow your doctor’s guidelines.



If you are taking the liquid form, use an accurate dosing syringe.

If you are taking the regular tablet, swallow it with a glass of water.

If you are taking an orally disintegrating tablet – then wait for it to dissolve in your mouth without chewing and swallow several times as the medicine melts in your mouth. Make sure that you use dry hands to hold this tablet and do not push it through the foil because you might damage it that way.



Lay down your entire medical history in front of your doctor. Typically, the diseases that you must report when taking this medicine are electrolyte imbalances, liver diseases, congestive heart failure or slower heartbeats, a personal/family history of long QT syndrome, a blockage in the digestive tract or any other sickness related to the stomach or the intestines.

The medicine is not known to be harmful to unborn babies but it is recommended that you inform your doctor beforehand. Similarly, it is uncertain whether the medication harms a nursing baby by passing through breast-milk and to be on the safe side, tell your doctor about your plan to breastfeed.

Do not use this medication for children younger than four years old.



You must report all your current medications to your healthcare provider to avoid harmful interactions – for example, Zofran should not be used simultaneously with apomorphine.

If you are allergic to ondansetron or to similar medicines then you must not take this medication.

Be cautious – inform your doctor if you have phenylketonuria (PKU) because the Zofran tablets may contain phenylalanine.

You can use laxatives to prevent or cure constipation caused by this drug.