June 9, 2022
5 min. read

Zofran for Nausea: Here’s What to Know About Side Effects, Dosage, and More


Good to Know:

  • Zofran is also called ondansetron. It’s a type of drug called an antiemetic, and it treats nausea and vomiting.
  • It’s often prescribed during cancer treatment or after surgery. It can also help treat morning sickness during pregnancy.
  • If your healthcare provider prescribes ondansetron, there are some common side effects you may experience.
  • There are also serious side effects you should look out for.


Nausea is a common side effect from cancer treatment, particularly chemotherapy and radiation treatment. But it’s also common to experience nausea while recovering from surgery, and roughly 8 out of 10 pregnant people cope with morning sickness during their first trimester. A common medication prescribed to treat nausea is Zofran.

If your healthcare provider has prescribed Zofran, here are some important facts to know. 

Did You Know? Ondansetron is included on the World Health Organization’s List of Essential Medicines.

What is ondansetron?

Ondansetron is also known by its brand name, Zofran. It’s a medication to treat nausea and vomiting. It’s most often prescribed after surgery or during cancer treatment. Specifically, ondansetron is often given to patients undergoing cancer chemotherapy or radiation therapy, but it can also be used to help prevent morning sickness during pregnancy. 

Zofran does not treat motion sickness.

Fast Facts: A 2018 study found that taking ondansetron during pregnancy did not seem to increase the risk of birth defects.

Ondansetron is part of a group of medications known as antiemetics. Antiemetics are medications that reduce or prevent nausea and vomiting.

How does ondansetron work?

Ondansetron is a type of antiemetic medication called a 5-ht3 receptor antagonists. 5-ht stands for 5-hydroxytryptamine, also known as serotonin. 5-ht3 receptors are located in your brain and your digestive system—in fact, 90% of your body’s serotonin exists in your gastrointestinal tract. Nausea is caused by serotonin getting released in your GI tract faster than it can be digested. The serotonin goes to a part of your brain called the chemoreceptor trigger zone, which is an important part of your vomiting reflex. The extra serotonin in your brain gets interpreted as nausea and feeling like you’re going to throw up.

Quick Statistics: 50% to 70% of patients with advanced cancer experience nausea as a side effect of chemotherapy treatment.

5-ht3 receptor antagonists block serotonin in both places, your brain as well as your GI tract. As a result, you stop feeling nauseated.

How should I take ondansetron?

Ondansetron can be taken four ways: a tablet, a rapidly dissolving tablet, a film, and a liquid solution. Store your medication at room temperature.

  • If taking ondansetron as a film, fold the pouch along the dotted line and tear the pouch along the edge. Don’t chew the film, but place it on your tongue to let it dissolve. It will take between 5 and 20 seconds, and you can swallow it with or without water.

  • If taking ondansetron as a rapidly disintegrating tablet, don’t push the tablet through the foil backing of the blister packet. Peel the foil backing and remove the tablet, then
    immediately place it on your tongue. It will dissolve in a couple of seconds, and you don’t need to drink anything to swallow it.

Quick Tips: If you vomit within 30 minutes of taking ondansetron, take the same amount of prescribed medication again. 

If you forget a dose, take the missed dose as soon as possible. The only exception to this is if your next dose is soon (i.e., you take ondenestron in the morning, and realize the missed dose the night before). Don’t take double the amount to make up for the missed dose, and always follow your healthcare provider’s dosing instructions.

Am I safe to take ondenestron?

Before you take this medication, let your healthcare provider know if you have any of the following conditions.

  • Allergic reactions to ondanestron, granisetron, or other medications
  • Heart disease, including a history of irregular heartbeat
  • Liver disease
  • Low magnesium levels
  • Low potassium levels

Can I take ondenestron while breastfeeding?

We recommend telling your healthcare provider know if you are pregnant or breastfeeding. While ondansetron is considered generally safe to treat morning sickness, you should still follow the medical advice of your healthcare provider. If they do not recommend taking ondenestron, you can discuss other options instead.

What are the side effects of ondansetron?

The most common side effects of Zofran include:

  • Constipation
  • Chills
  • Diarrhea
  • Drowsiness or tiredness
  • Headaches
  • Weakness

If you experience the following symptoms, tell your healthcare provider immediately, or seek emergency medical attention.

  • Blurred vision or vision loss
  • Rash, hives, itching, or other signs of a possible allergic reaction
  • Seizures
  • Serotonin syndrome

Quick Tips: Alert your doctor if you take antidepressants or use certain over-the-counter supplements such as ginseng or St. John’s Wort. These can increase your risk of serotonin syndrome.

Are there serious side effects to ondansetron?

There can be, which is why it’s important to discuss any previous health conditions with your healthcare provider. Specifically, alert your doctor if you or anyone in your family has been diagnosed with long QT syndrome. Long QT syndrome is a heart condition that can cause fast, irregular heartbeat. The most common symptom is fainting, but many people don’t show any symptoms. You can receive a diagnosis through an electrocardiogram, genetic testing, or based on your family history. 

The U.S. Food and Drug Administration (FDA) released a statement in 2012 that ondansetron may affect your heart rate, causing something called QT interval prolongation. If you experience irregular heartbeat, dizziness, trouble breathing, or lightheadedness, alert your doctor as soon as possible. You can see the FDA’s full statement at fda.gov.


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