What Pharmacists Say About How Long Zofran Takes to Work (Plus 4 More Tips)

If you've ever experienced nausea or vomiting (N/V), you know how uncomfortable and disruptive it can be. And it's always a relief when it's prevented or goes away. Thankfully, when needed, certain medications can step up and relieve these symptoms.

Zofran (ondansetron) is a popular choice to prevent N/V. However, taking it isn’t always straightforward. You may be wondering how long it takes to work. Or whether to take it with food. We’ll answer those questions, and others, to help you get the most out of your Zofran prescription.

What is Zofran?

Zofran is a prescription medication that’s FDA approved to prevent N/V from cancer medications, radiation treatments, and surgical procedures. It's also used off-label for many other health conditions, such as pregnancy-related nausea and gastroenteritis. 

It's available in many dosage forms. It comes as a regular tablet, an orally disintegrating tablet, an oral liquid, and as an injection given into your muscle or vein. Your specific Zofran form and dose will vary depending on your situation and medical history. 

Zofran works by blocking serotonin from binding to certain receptors (chemical binding sites) throughout your brain and body. Serotonin is an important chemical that helps our nerves communicate — including communicating to our brain that we’re feeling nauseated. By blocking these receptors, serotonin sends fewer signals that cause N/V.

5 pharmacist-backed tips for taking Zofran

Below, we offer five helpful tips to keep in mind if you have a prescription for Zofran. If you have specific questions about how to take Zofran, be sure to talk to your pharmacist.

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1. How long does it take Zofran to work?

Zofran is quickly absorbed into your body. If you’re taking oral Zofran, it usually starts working within 30 minutes. However, it may take up to 2 hours to reach its full effects.

In general, it’s recommended to take Zofran before you experience N/V symptoms. You should take it prior to receiving your nausea-causing medication or medical procedure. This gives the medication enough time to start working. 

2. Should I take Zofran with food?

Zofran can be taken with or without food. 

Taking Zofran with a meal or snack may slightly enhance its effects, but eating may not be realistic if you’re already feeling nauseated. It's also important to remember that your healthcare provider may tell you not to eat before certain cancer treatments or surgery. Make sure to follow their directions.

3. Should I separate Zofran from any medications or foods?

No, you don't have to separate Zofran from other medications or foods. But Zofran has some interactions to be aware of that can happen regardless of when you take it throughout the day. Below are top examples of medications that can interact with Zofran.

Medications that raise serotonin levels

As discussed earlier, Zofran blocks serotonin from binding to some receptors. And less serotonin stuck to receptors means there’s more of it hanging around. Many medications aside from Zofran can also increase your serotonin levels. Common examples are medications used to treat anxiety and depression, like sertraline (Zoloft) and venlafaxine (Effexor XR). Other types of medications that raise serotonin levels include triptan migraine medications, antibiotics like linezolid (Zyvox), and more. 

When combined with Zofran, these medications can make your serotonin levels too high. In some cases, this can lead to serotonin syndrome. Most cases of serotonin syndrome are mild, causing symptoms like trouble sleeping, shakiness, and excessive sweating. But more severe symptoms are also possible. This is discussed more later on.

Heart rhythm medications

Although rare, Zofran can affect your heartbeat. There have been reports of QT prolongation, which is a dangerous condition that affects your heart’s electrical activity. This is more common in people with low blood levels of potassium or magnesium, people receiving high doses of Zofran, or people taking other medications that affect your heart rhythm (antiarrhythmics). 

If you take other medications that affect your heart rhythm, it’s important to use caution while taking Zofran. One example is a heart rhythm medication called amiodarone (Pacerone). Both medications can lengthen the amount of time between heartbeats, possibly resulting in dizziness and fainting. Many other medications can also have this effect.

Certain antibiotics

Certain antibiotics can also prolong the QT interval. Taking fluoroquinolone or macrolide antibiotics (like ciprofloxacin or azithromycin) with Zofran can cause a higher chance of an irregular heartbeat.

This isn't a complete list of all possible Zofran interactions. Make sure your pharmacist and healthcare provider know about all medications you take before you start taking Zofran. Try to give them an updated medication list, which should include all prescription medications, over-the-counter medications, and supplements you take.

4. What happens if I miss my dose of Zofran?

Your healthcare provider may direct you to take Zofran as needed, or at scheduled times throughout the day. If you’re taking Zofran just when you need it, there aren’t any concerns about a missed dose. 

However, if you miss a scheduled dose of Zofran, try to take it as soon as you remember. If it's almost time for your next dose, skip the dose you missed and take the next one as scheduled. You should avoid taking two doses of Zofran at one time unless otherwise instructed. This could lead to a dose that's too high and increase your risk of side effects.

5. What can I do if I experience side effects from Zofran?

Zofran has a number of common side effects, including:

• Headache

• Tiredness

• Constipation

• Diarrhea

If you experience mild side effects like these after starting Zofran, consider reaching out to your healthcare provider. They may adjust your dose or offer tips to manage side effects. But you should contact them right away if any side effects become bothersome or don't go away.

Zofran can also cause some rare but serious side effects:

• Serotonin syndrome: Symptoms of serotonin syndrome vary depending on the severity of the condition. But if you experience symptoms like high fever, uncontrollable body movements, or intense diarrhea, seek immediate medical attention.

• Heart rhythm problems: As mentioned, Zofran can sometimes cause heart rhythm problems. Call your healthcare provider immediately if you feel lightheaded or feel an irregular heartbeat.

• Bowel obstruction: Zofran can mask (hide) symptoms of certain bowel problems. As a precaution, contact your healthcare provider right away if you have possible symptoms of a bowel obstruction, like abdominal pain with bloating.

• Allergic reactions: As with any medication, it's possible to be allergic to Zofran. You should stop taking it and contact your healthcare provider if you have signs of an allergic reaction (e.g., hives or itching). And if your symptoms are severe and include trouble breathing, seek medical attention right away. 

Tips on how to save money with your Zofran prescription

There are ways to save on Zofran, which is available as a lower-cost generic medication. GoodRx can help you save over 98% off the average retail price of the generic version. Generic Zofran at certain pharmacies is less than $2 with a free GoodRx discount.

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Written by:

Nikki Javit, PharmD

Nikki Javit, PharmD, is a clinical pharmacist with certifications in international travel medicine, immunization delivery, and pharmacogenomics. She received her bachelor’s of science in biology from Indiana University Bloomington and her doctor of pharmacy degree from Butler University.

Edited by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

Reviewed by:

Tegan Smedley, PharmD, APh

Tegan Smedley, PharmD, APh, has 10 years of experience as a pharmacist. She has worked in a variety of settings, including retail, hospital, and ambulatory care.

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