Ondansetron (Zofran) Dosages: Your GoodRx Guide

Everyone experiences nausea from time to time. In many cases, it’s mild and improves on its own. But sometimes it’s severe enough that you may need medication to relieve your symptoms. That’s where ondansetron (Zofran) can help. It’s a prescription medication used to prevent nausea and vomiting.

The right ondansetron dosage for you varies based on your age and what you’re taking it for. Here, we’ll review the recommended ondansetron dosages for adults and children. Keep in mind that your prescriber may adjust your dosage based on your personal history. So it’s best to follow their instructions, even if it differs from what’s described below.

What’s the typical ondansetron dosage for adults?

The usual ondansetron dosage for adults depends on what you’re taking it for. It’s FDA approved to prevent nausea and vomiting caused by certain cancer treatments or surgery. The maximum daily dose of ondansetron for adults is 24 mg per day.

Ondansetron is also prescribed off-label for other types of nausea, such as nausea caused by migraines, pregnancy, or vertigo. There aren’t FDA-approved dosages for off-label use, so these uses won’t be covered in this article.

Highly emetogenic cancer therapy

For highly emetogenic chemotherapy, the typical ondansetron dosage is 24 mg taken 30 minutes prior to your chemotherapy treatment.

“Highly emetogenic” simply means chemotherapy treatments that are known to cause nausea in more than 90% of people who receive them. Examples include cisplatin (Platinol) and dacarbazine.

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Moderately emetogenic cancer therapy

For moderately emetogenic chemotherapy, the recommended ondansetron dosage is 8 mg taken 30 minutes before chemotherapy starts. Then, you’ll take another 8 mg dose 8 hours later. After that, you’ll continue taking 8 mg of ondansetron every 12 hours for 1 to 2 days after finishing chemotherapy. Your prescriber will let you know exactly how long to continue taking it.

“Moderately emetogenic” chemotherapy treatments typically cause nausea and vomiting in 30% to 90% of people who take them. Examples include carboplatin (Paraplatin) and doxorubicin (Doxil).

Radiation

Radiation therapy can also cause nausea. The ondansetron dosage for nausea caused by radiation therapy depends on the type of radiation you’re receiving:

• Total body radiotherapy: 8 mg daily, 1 to 2 hours before each radiotherapy treatment

• Single high-dose radiotherapy to the abdomen: A single 8 mg dose 1 to 2 hours before radiation treatment, then 8 mg every 8 hours for 1 to 2 days

• Daily radiation treatment to the abdomen: A single 8 mg dose 1 to 2 hours before each radiation treatment, then 8 mg every 8 hours for the remainder of the day

Postoperative use

To prevent nausea after surgery, the recommended ondansetron dosage is 16 mg taken 1 hour before anesthesia is started.

What’s the typical ondansetron dosage for children?

Ondansetron is FDA approved for children as young as 4 years of age that are receiving moderately emetogenic chemotherapy. Unlike many other medications, oral Zofran dosages for children aren’t based on their body weight. Instead, your child’s age determines their dosage. Daily doses of ondansetron over 24 mg aren’t recommended, and in most cases children will take 16 mg per day or less.

Moderately emetogenic cancer therapy

The recommended ondansetron dosage to prevent nausea from chemotherapy in children is as follows:

• Ages 4 to 11 years: One 4 mg dose 30 minutes before starting chemotherapy. Then another 4 mg dose 4 hours and 8 hours after the first dose. After that, the dose is 4 mg 3 times daily for 1 to 2 days after finishing chemotherapy.

• Ages 12 to 17 years: One 8 mg dose 30 minutes before starting chemotherapy. Then another 8 mg dose 8 hours later. After that, the dose is 8 mg every 12 hours for 1 to 2 days after finishing chemotherapy.

EXPERT PICKS: WHAT TO READ NEXT

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• Zofran side effects: Here are common and rare side effects to watch out for while taking Zofran.

What dosage forms does ondansetron come in?

Ondansetron comes in three different oral dosage forms. It’s available in oral tablets, orally disintegrating tablets (ODTs), and an oral solution (liquid). The products are interchangeable, meaning that your dosage will be the same regardless of which form you’re prescribed. 

ODTs or the oral solution may be better options for children or adults who have trouble swallowing tablets.

Ondansetron also comes in an injectable dosage form. But it’s usually only administered in hospitals or clinics by a healthcare professional. So we aren’t including its dosages here.

The table below shows the available doses for oral forms of ondansetron.

Swallow ondansetron tablets whole. The ondansetron ODTs are designed to dissolve in the mouth. Place the ODT in your mouth on top of your tongue. It will dissolve in seconds, and you can swallow normally after that. You don’t need to take ODTs with any liquid.

Ondansetron ODTs are fragile, so you shouldn’t try to push them through the foil backing, as they’re likely to crumble under pressure. This may make it hard for you to take the full dose. Instead, gently peel back the foil before removing the tablet from the blister package. Be sure to use dry hands to remove the tablets. Moisture on your hands can make them dissolve while you’re holding them. Also, don’t remove any tablets from the packaging until you're ready to take your dose.

Ondansetron oral solution is strawberry flavored, and you should store it at room temperature. You don't need to shake it before you use it. But you should use the included dosing cup or syringe to measure the liquid. Your pharmacist can provide a replacement if needed. Don’t use a household measuring spoon — they aren’t designed to measure liquid medications accurately.

Are there any dosage adjustments for medical conditions?

For people with severe liver problems, the maximum dose of ondansetron is lowered to 8 mg per day. There’s no dose adjustment needed for people with kidney problems or mild to moderate liver problems. If you have liver problems, your prescriber will determine whether you need a lower dose of ondansetron.

What happens if you miss a dose of ondansetron?

Generally, you should take a missed dose of ondansetron as soon as you remember. But if it’s almost time for your next dose, skip the missed dose. Then, return to your usual dosing schedule. You shouldn’t take two doses at once to make up for a missed dose.

If you miss more than one dose of ondansetron, it’s a good idea to check in with your prescriber. They can let you know the best way to return to your regular schedule.

What should you do if you take too much ondansetron?

While taking too much ondansetron is unlikely to cause serious problems, you still want to make sure you take it exactly as prescribed. Taking too much ondansetron can lead to increased side effects, such as headache and diarrhea or constipation.

An ondansetron overdose in children can be more dangerous. One case report of an overdose in an infant noted severe symptoms, including seizures, heart issues, and liver damage. Serotonin syndrome may also occur after taking too much ondansetron. Symptoms of serotonin syndrome can include agitation, sweating, and seizures.

If you take more ondansetron than prescribed, it’s a good idea to let your healthcare team know or contact Poison Control at 1-800-222-1222. But if you have severe symptoms, or if your child takes more ondansetron than prescribed, call 911 or seek emergency care right away.

How to save on ondansetron

There are ways to save on ondansetron tablets, ODTs, and oral solution, which are all only available as lower-cost generics.

GoodRx can help you save over 80% off the average retail price of the generic tablets. The cost of 20 ondansetron 4 mg tablets at certain pharmacies is as low as $4.00 with a free GoodRx discount. The same supply of ondansetron ODTs costs as little as $9.40. And with a GoodRx discount, a 50 mL bottle of the ondansetron oral solution costs as little as $28.77. 

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Written by:

Austin Ulrich, PharmD, BCACP

Austin Ulrich, PharmD, BCACP, is a board-certified ambulatory care clinical pharmacist. In his early career, he provided direct patient care in a variety of settings, including hospital and community pharmacies, and in a primary care clinic as a clinical pharmacist.

Edited by:

Stacia Woodcock, PharmD

Stacia Woodcock, PharmD, is a pharmacy editor for GoodRx. She earned her Doctor of Pharmacy degree from the University of Kentucky and is licensed in New York and Massachusetts.

Reviewed by:

Amy B. Gragnolati, PharmD, BCPS

Amy Gragnolati, PharmD, BCPS, is a pharmacy editor for GoodRx. Amy currently holds her pharmacist license in Georgia and California.

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