Zofran Side Effects

As of June 30, 2024, the U.S. Food and Drug Administration classified nearly two-thirds of adverse event reports it received as serious. These included maternal and fetal exposure during pregnancy.

Common side effects associated with Zofran (ondansetron) include nausea, pain, headache, constipation, anxiety and vomiting. Other common reports concern the ineffectiveness of the medication.

Disclaimer: Reports sent to the FDA don’t necessarily mean the drug caused an adverse event. Consult a health care professional before stopping or changing medication.

Zofran FDA Warnings and Precautions

Zofran is associated with a greater risk of developing an irregular heart rhythm known as QT prolongation. The FDA issued safety advisories about this risk in 2011 and 2012.

Patients with an allergy to ondansetron or those on apomorphine, a drug used to help manage Parkinson’s symptoms, should not take Zofran. Some patients on Zofran may develop serotonin syndrome, where the body produces too much serotonin. This can cause shivering, diarrhea, loss of muscle control and seizures.

Both serotonin syndrome and QT prolongation can be fatal if untreated.

Zofran can mask the symptoms of gastric swelling, bloating or reduction in bowel activity in patients who take the drug after abdominal surgery or to treat nausea from chemotherapy. These patients should closely monitor their bowel activity and report decreased activity to their doctor.

Some people who take Zofran may feel severe nausea after a dosage. Other possible side effects include chills, drowsiness and weakness. However, even the most reported side effects are rare and typically only last a few days. Patients should talk to their doctor if symptoms persist any longer.

Patients with a history of heart disease, irregular heartbeat, allergies to ondansetron or low levels of magnesium or potassium have a higher risk of experiencing side effects.

Data concerning Zofran’s effects on pregnant or breastfeeding people is inconsistent. Pregnant or breastfeeding patients should consult with their doctor before starting Zofran.

Severe but rare side effects of Zofran include allergic reaction, abnormal heart rhythm and serotonin syndrome.

Patients can develop symptoms of myocardial ischemia, a blockage of the coronary artery, with oral or intravenous administration of Zofran. This is an elevated risk for patients with known coronary artery spasms.

Some patients can experience hypersensitivity reactions, including narrowing of the airways and anaphylaxis. A 2021 case report published in Clinical Case Reports describes an event in which a patient received a dose of Zofran and subsequently died from an allergic reaction. This patient had not been taking any medications that would interact with Zofran and had no history of allergies. The report discusses the need for more awareness and monitoring of the possibility of allergic reaction.

Patients exhibiting any of these reactions while taking Zofran should get immediate medical attention. Anyone who has previously had an allergic reaction to a 5-HT3 receptor antagonist, such as granisetron or palonosetron, should discuss this with their doctor before using Zofran.

Abnormal Heart Rhythms, Including QT Prolongation

The FDA reports that some people who take Zofran can develop irregular heart rhythms. Arrhythmias may include fast heart rate (tachycardia), slow heart rate (bradycardia) or fast heartbeats that originate from the wrong part of the heart (ventricular and supraventricular tachycardia).

Long QT syndrome is another serious and potentially deadly heart problem. People who were born with long QT syndrome should not take Zofran. Doctors should closely monitor patients on Zofran who take medications known to lead to QT prolongation, have congestive heart failure, have a slow heart rate or have low magnesium or potassium levels.

Serotonin Syndrome

Zofran may cause a rare but serious condition called serotonin syndrome or serotonin toxicity, which occurs from an overactive production or accumulation of serotonin. The risk increases for patients taking other medications that increase serotonin levels, such as certain classes of antidepressants like selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs).

Other symptoms of serotonin syndrome include severe dizziness, diarrhea, loss of coordination and fever. In serious cases, serotonin syndrome can cause coma, irregular heartbeat, seizures, unresponsiveness and death.

Some patients take Zofran to treat nausea and morning sickness during pregnancy, but this is an off-label use. Patients have filed hundreds of Zofran lawsuits against the drug’s manufacturer GlaxoSmithKline, alleging that the medication caused birth defects in their babies. Plaintiffs also claim the company advertised Zofran as a morning sickness treatment, despite this being an off-label use.

However, in 2021, Obstetrics and Gynecology published the results of a large study of over 456,963 pregnancies in three countries. This research found no increased risk of birth defects from ondansetron compared to other anti-nausea drugs.

This followed a 2019 review and analysis published in Reproductive Toxicology that showed no correlation between Zofran use during pregnancy and birth defects. However, the researchers did recommend further analysis.

Some medications and supplements, especially certain sedatives, muscle relaxers and anti-depressants, have drug interactions with Zofran. Alcohol and illegal drugs can also interact with Zofran. Patients should inform their doctor of everything they take, including non-prescription drugs and herbs.

Knowing a patient’s medical history, medications, supplements and lifestyle can help doctors determine the correct medications to administer to lower the risk of interactions or adverse side effects. If any new symptoms occur after starting Zofran, patients should contact their doctor for advice and seek medical treatment if necessary.

The American Cancer Society lists several anti-emetic alternatives to Zofran.

Every medication can cause side effects or adverse reactions. The best alternative medication depends on your symptoms, diagnosis, medical history and risk factors.

Editor Lindsay Donaldson contributed to this article.