Generic Ondansetron

Common use

Ondansetron is an anti-nausea medication used to prevent and treat nausea and vomiting caused by chemotherapy, radiation therapy, and surgery. It works by blocking serotonin, a natural substance in the body that triggers vomiting. Ondansetron is commonly used in cancer patients undergoing treatment and in postoperative care. It is effective for both preventing and relieving active nausea symptoms.

Dosage and direction

Ondansetron is usually taken orally as a tablet, disintegrating tablet, or oral solution, depending on the form prescribed. The dosage varies based on the cause of nausea, age, and overall health status. It’s typically given 30 minutes before chemotherapy or surgery and may be repeated at regular intervals. Always follow your doctor’s instructions carefully for timing and dosing.

Precautions

Before using ondansetron, inform your doctor if you have liver problems, electrolyte imbalances, or a history of heart rhythm disorders. It can cause QT prolongation, a potentially serious heart rhythm condition, especially in those with existing cardiac risk factors. Use caution if pregnant or breastfeeding—consult with your healthcare provider first. Dehydration and electrolyte abnormalities should be corrected before starting treatment.

Contraindications

Ondansetron is contraindicated in patients with known hypersensitivity to ondansetron or any of its components. It should not be used with apomorphine due to the risk of profound hypotension and loss of consciousness. People with congenital long QT syndrome should avoid using this medication. Medical supervision is required for those with severe hepatic impairment.

Possible side effect

Common side effects include headache, constipation, dizziness, and fatigue. Some patients may experience a temporary rise in liver enzymes or a feeling of warmth or flushing. Rare but serious side effects can include abnormal heart rhythms or allergic reactions such as rash and swelling. Seek immediate medical help if you experience chest pain, fainting, or signs of a severe allergic reaction.

Drug interaction

Ondansetron may interact with medications that affect heart rhythm such as certain antiarrhythmics, antidepressants, and antipsychotics. It may also interact with drugs that alter serotonin levels like SSRIs or MAO inhibitors, increasing the risk of serotonin syndrome. Inform your doctor about all prescription, over-the-counter, and herbal medications you are taking. Adjustments may be required to avoid complications.

Missed dose

If you miss a dose of ondansetron, take it as soon as you remember unless it’s close to the time for your next dose. Do not take two doses at once to make up for a missed one. For scheduled chemotherapy, follow your treatment team’s guidance. Consistency is important for effectiveness in prevention.

Overdose

Overdose symptoms may include severe dizziness, fainting, or irregular heartbeat. In case of overdose, seek emergency medical attention immediately. Treatment usually involves supportive care in a clinical setting. Do not exceed the prescribed dosage.

Storage

Store ondansetron at room temperature, away from moisture and heat. Keep it in its original container, tightly closed, and out of the reach of children. Do not use the medication after the expiration date. Ask your pharmacist how to properly dispose of unused medicine.

Disclaimer

We provide only general information about medications which does not cover all directions, possible drug integrations, or precautions. Information at the site cannot be used for self-treatment and self-diagnosis. Any specific instructions for a particular patient should be agreed with your health care adviser or doctor in charge of the case. We disclaim reliability of this information and mistakes it could contain. We are not responsible for any direct, indirect, special or other indirect damage as a result of any use of the information on this site and also for consequences of self-treatment.

Clinical Verification

Last Clinically Updated: August 15, 2026

Written By

Dr. Elena Vance, PharmD

Clinical Specialist in Neuropharmacology

Fact Checked By

Marcus Thorne, MS

Biomedical Data & FDA Label Verification

Medically Reviewed By

Dr. Arthur Campbell, MD

Board-Certified Psychiatrist (ABPN)