Key takeaways:
Ondansetron (Zofran) is a medication that helps prevent nausea and vomiting from chemotherapy, radiation treatment, or surgery.
The recommended ondansetron dosage depends on your age and what you’re taking it for. A typical ondansetron dose is 8 mg to 24 mg for adults and adolescents and 4 mg for children under the age of 12. Doses over 24 mg per day aren’t recommended.
Oral ondansetron comes as a tablet, an orally disintegrating tablet, and an oral solution. Your dosage will be the same no matter which of these forms you take.
Ondansetron is available as a lower-cost generic. GoodRx can help you save over 80% off the average retail price at certain pharmacies.
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Everyone experiences nausea from time to time. In many cases, it’s mild and improves on its own. But severe nausea and vomiting can be hard to treat once it starts. 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.
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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.
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 that round of 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
After surgery
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 ages 4 and older 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 the last day of 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 that round of chemotherapy.
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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.
Tablets | ODTs | Oral Solution |
4 mg 8 mg 24 mg | 4 mg 8 mg 16 mg 24 mg | 4 mg/5 mL |
How to take 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. Do not chew the ODT — it will dissolve within 1 minute, and you can swallow normally after that. You don’t need to take ODTs with any liquid. And you can take ondansetron tablets or ODTs with or without food.
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, caused by too much serotonin in the body, 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 $10.60. And with a GoodRx discount, a 50 mL bottle of the ondansetron oral solution costs as little as $28.04.
Frequently asked questions
Yes, ondansetron can interact with other medications. Taking ondansetron with antidepressants, such as selective serotonin reuptake inhibitors (SSRIs), can increase the risk of serotonin syndrome. It can also interact with certain antibiotics and heart rhythm medications, raising the risk of an irregular heartbeat called long QT syndrome.
Ondansetron works quickly, in most cases within 30 minutes. But it may take up to 2 hours for it to reach its full effect. It’s best to take ondansetron before medications or procedures that cause nausea. It works better to prevent nausea than to treat it once it occurs.
Ondansetron works by blocking serotonin receptors (binding sites) that are involved in nausea and vomiting. This helps prevent signals that stimulate the nausea centers of the brain.
It's not a common side effect, but ondansetron may cause drowsiness for some people. It may also make you feel weak or fatigued in some cases. Keep in mind that the conditions behind your nausea can also cause fatigue. So it may be related to more than ondansetron itself. Still, it’s best to avoid driving or other activities that require alertness after taking ondansetron until you know how it affects you.
Yes, ondansetron can interact with other medications. Taking ondansetron with antidepressants, such as selective serotonin reuptake inhibitors (SSRIs), can increase the risk of serotonin syndrome. It can also interact with certain antibiotics and heart rhythm medications, raising the risk of an irregular heartbeat called long QT syndrome.
Ondansetron works quickly, in most cases within 30 minutes. But it may take up to 2 hours for it to reach its full effect. It’s best to take ondansetron before medications or procedures that cause nausea. It works better to prevent nausea than to treat it once it occurs.
Ondansetron works by blocking serotonin receptors (binding sites) that are involved in nausea and vomiting. This helps prevent signals that stimulate the nausea centers of the brain.
It's not a common side effect, but ondansetron may cause drowsiness for some people. It may also make you feel weak or fatigued in some cases. Keep in mind that the conditions behind your nausea can also cause fatigue. So it may be related to more than ondansetron itself. Still, it’s best to avoid driving or other activities that require alertness after taking ondansetron until you know how it affects you.
The bottom line
Ondansetron (Zofran) is a medication that helps prevent nausea and vomiting caused by chemotherapy, radiation, or surgery. It comes as an oral tablet, an orally disintegrating tablet, and an oral solution.
Your ondansetron dosage depends on what type of nausea you’re treating. But a typical ondansetron dose is 8 mg to 24 mg for adults and adolescents and 4 mg for children under age 12. Doses over 24 mg per day aren’t recommended. Your prescriber will help determine the right ondansetron dosage for you.
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References
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National Cancer Institute. (2025). Nausea and vomiting related to cancer treatment (PDQ)-health professional version.
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