Ondansetron, also found under the brand name Zofran®, is a prescription medication used to help prevent and control nausea and vomiting.¹ It works by blocking signals in the body that trigger nausea, helping many adults reduce discomfort and feel more able to go about their day.

Here’s what to know about how ondansetron works, how to use it and what to expect.

• Ondansetron helps prevent nausea and vomiting.

• It is available in oral tablets, orally disintegrating tablets (ODTs), dissolvable film and liquid.

• Dosing depends on the cause of the nausea and your provider’s instructions.
  

Ondansetron (Zofran^®) Overview

Ondansetron is a prescription antinausea medication in a drug class called serotonin 5-HT₃ receptor antagonists. It is used to prevent nausea and vomiting, and works by blocking serotonin, a natural chemical in the body that can trigger these issues.

The medication comes in several forms, the most common being oral tablets or orally disintegrating tablets (ODT) that dissolve on the tongue. But it can also be injected or found as a liquid or dissolvable film.^2,3

Ondansetron Dosages for Adults

Dosages will depend on the form of ondansetron being taken, and the age and health of the patient. Typically, the tablets and ODTs come in strengths of 4 mg and 8 mg, with 16 mg and 24 mg doses available for more severe cases of nausea and vomiting.⁴

When to Take Ondansetron

When possible, clinicians often recommend taking ondansetron 30 minutes to one to two hours before a known nausea trigger. Always follow your healthcare provider’s specific instructions when taking any medication.⁵

How Quickly Ondansetron Works

Ondansetron tablets and ODTs typically begin working within about 30 minutes, though its effects are typically strongest around an hour and a half after taken.⁶ That’s why it is taken ahead of time when nausea is expected.

How Often to Take Ondansetron

The number of doses you take each day, the time allowed between doses and the length of time you take the medicine depends on a few factors, including the reason the medicine was prescribed and the strength of each dose. Always follow your healthcare provider’s instructions when taking medication.⁷

How Long Ondansetron Effects Last

The effects typically last eight to 12 hours, but this can vary by person.⁸

Maximum Daily Ondansetron Dosage for Adults

The prescribed daily dose depends on the reason for use and the health of the patient taking the medicine, but the maximum daily dosage for adults is limited to 24 mg per day.⁹ Never exceed the amount prescribed by your healthcare provider.

Ondansetron Use During Pregnancy

Ondansetron can be prescribed to treat nausea and vomiting related to morning sickness. It has not been shown to be harmful during pregnancy, but you should discuss your symptoms and the risks of the medication with your healthcare provider if you are interested in ondansetron.^10,11

Ondansetron Side Effects and Safety

Minor side effects from taking ondansetron may include:

• Headache

• Constipation

• Weakness

• Chills

• Drowsiness or lack of energy

In rare cases, more severe side effects may occur:

• Blurred vision or vision loss

• Rash

• Hives

• Itching

• Swelling of the eyes, face, lips, tongue, throat, hands, feet, ankles or lower legs

• Hoarseness

• Difficulty breathing or swallowing

• Chest pain

• Shortness of breath

• Dizziness, light-headedness or fainting

• Fast, slow or irregular heartbeat

• Agitation

• Hallucinations (seeing things or hearing voices that do not exist)

• Fever

• Excessive sweating

• Confusion

• Nausea, vomiting or diarrhea

• Loss of coordination

• Stiff or twitching muscles

• Seizures

• Coma (loss of consciousness)

Call your doctor if you have any persistent minor side effects while you are taking this medication, or immediately if you experience a more severe reaction.¹²

How RedBox Rx Can Help

There are options for nausea and vomiting relief, and RedBox Rx offers a variety of FDA-approved prescription medications. Your first step toward relief is to start an online consultation with one of our experienced, licensed medical providers.

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