Nausea During Pregnancy: Is Zofran Safe?

By Jeffrey Boyle, MD Jun 04, 2015

Have you seen the TV ads telling you to call a lawyer because Zofran causes birth defects? Well, let’s look at the facts.

What is Zofran?

Zofran is a medication that is often prescribed for morning sickness during pregnancy. The official medical name for Zofran is ondansetron. It works by blocking serotonin receptors in the brain, which helps suppress the feeling of nausea.

Zofran was originally used to treat nausea and vomiting in patients undergoing chemotherapy and radiation treatments and was later found to be helpful to pregnant women with morning sickness.

Patient Studies of Zofran

Whether or not a medication can be safely used in pregnancy is usually first determined by studies. Unfortunately, there are not many quality studies on Zofran because they are difficult to do on pregnant women.

The first reports were of a few individual patients trying Zofran because of severe symptoms. The symptoms improved and they had good pregnancy outcomes. Eventually, a few small studies were done that showed Zofran was safe and effective compared to other medications used for morning sickness. However, these studies were too small to make any definite conclusions.

A study in 2012, using information from the National Birth Defects Prevention Study in the U.S., found an association between the use of Zofran and the development of cleft palates. However, it involved only 55 patients and because of a weak study design, the results were questionable.

There are three, recent large studies that provide the best information we have on the safety of Zofran use during pregnancy.

The first study was important in showing no complications in pregnancy from Zofran, but the question of birth defects was not quite answered because half of the patients started Zofran after 10 weeks gestation, which is after the critical time for organ development in the embryo.

The second large study included more patients over a greater period of time. In contrast to the previous report, it showed an increased risk of heart defects from the use of Zofran in the first trimester.

The most recent and largest study to date was published in 2014 and included 1,349 women.The study concluded that the use of Zofran in early pregnancy is not associated with a high risk of birth defects but that an increased risk of heart defects “may exist.” Therefore, the authors recommend not using Zofran for nausea and vomiting in early pregnancy until further research is available.

The American College of Obstetricians and Gynecologists (ACOG) has said there is limited evidence on the safety of Zofran for nausea and vomiting of pregnancy, particularly in the first trimester, and recommends the use of Zofran only after all other first-line medications have been tried.

The most common side effects of Zofran include headache, fatigue, constipation and drowsiness. Because Zofran can cause arrhythmias, caution should be used in patients with a personal or family history of arrhythmia, low potassium, low magnesium or heart failure.

Use of Zofran in Pregnancy

What does all of this information tell us about the use of Zofran in pregnancy?

  • There is no proof that Zofran causes an increased risk of birth defects overall.
  • Zofran is safe in pregnancy after 10 to 12 weeks gestation.
  • A few studies have shown a small increased risk of minor heart defects in babies.
  • The true risk of Zofran is not yet known because the available studies are not the best quality.
  • Zofran should be used for nausea and vomiting in pregnancy only after other medications have been tried.

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