Researchers studying the risks of the popular anti-nausea medication Zofran (ondansetron) observed an increased risk of cardiac birth defects in children born to mothers who took the drug during pregnancy.

The study concluded that Zofran should not be used as an off-label treatment for morning sickness.

Published in the medical journal Reproductive Toxicology in December 2014, the Zofran birth defect study consisted of data from the Swedish Medical Birth Register and the Swedish Register of Prescribed Drugs.

Overview of Zofran Birth Defects Study

The study looked at over 1.5 million births, approximately 1,349 of which were babies born from 1998 to 2012 whose mothers took Zofran during early pregnancy.

The infants were identified through two sources — midwife interviews at the mother’s first prenatal care visit, where the mothers’ answers about what drugs they used since becoming pregnant were entered into the Medical Birth Register, and the Swedish Prescribed Drug Register, which identified what drugs the mothers were prescribed.

The study showed that Zofran use in early pregnancy may carry an increased risk for cardiac defects, particularly a cardiac septum defect.

The researchers concluded that further studies were needed to adequately determine the true risk of Zofran birth defects, and whether the drug carried a higher risk of cardiac malformations than other defects such as cleft palate.

Zofran was originally approved to treat severe nausea and vomiting after chemotherapy or surgery. According to some Zofran lawsuits, however, Zofran’s manufacturer GlaxoSmithKline allegedly marketed Zofran off-label, or for a purpose different from that described in the FDA-approved drug label, to treat morning sickness.

The company paid three billion dollars to the U.S. Department of Justice to settle criminal and civil penalties in 2012. This amount was to settle the allegations of illegally advertising Zofran to pregnant women, and for allegedly paying kickbacks to physicians to prescribe the medication.