Swedish researchers have added to the growing body of evidence that suggests the nausea medicine Zofran may be a major risk factor for birth defects.

Zofran is a powerful anti-nausea medication; however, the U.S. Food and Drug Administration (FDA) has only approved Zofran for treating nausea associated with surgical anesthesia and radiation therapy. Despite these restrictions, under U.S. law, physicians can prescribe a drug beyond its FDA approval, commonly referred to as off-label prescription use. However, drug makers themselves are strictly forbidden from promoting a drug for off-label uses. The makers of Zofran have been punished by the federal government for promoting their drugs for the off-label of morning sickness in pregnant women.

Off-label use of Zofran is of special concern to women who are pregnant or hoping to become pregnant. Since it is an anti-nausea drug, a physician may prescribe Zofran off-label for morning sickness. However, a growing body of evidence suggests a risk of Zofran birth defects, potentially making this type of off-label treatment unwise and unsafe.

Zofran Birth Defects Studies

The latest evidence comes from a research paper published in the peer-reviewed medical journal Reproductive Toxicity. The journal article reported on a study wherein researchers from Sweden collected data from the Swedish Medical Birth Registry and the Swedish Register of Prescribed Drugs between 1998 and 2012. Based on this data, researchers were able to find data for 1,349 infants born to women who took Zofran.

When researchers compared data from women who took Zofran during pregnancy to women who didn’t, they found that women who took Zofran during pregnancy were much more likely to have children with birth defects.

Specifically, researchers found an increased risk of artial septal defects and ventral septal defects, types of heart defects. In these types of heart defects, the walls dividing the chambers of the heart do not fully form. This causes the heart to under-perform and ultimately leads to the mixing together oxygenated and un-oxygenated blood together. At minimum, ventricular septal defects and atrial septal defects are medical emergency and may require surgical intervention. These Zofran birth defect conditions can be fatal. Additionally, women taking Zofran during pregnancy were 62 percent more likely to develop heart defects.

Curiously, the study found no evidence of a more general risk of Zofran birth defects: only heart defects, including both atrial septal defects and ventricular septal defects were observed. Researchers concluded that Zofran should not be prescribed during pregnancy due to the risk of Zofran birth defects that affect the unborn child’s heart.

Other preliminary studies found a more general risk of Zofran birth defects. A sample size of less than 1,500 is relatively small, and may not have had powerful enough statistical power to identify the risk of other possible Zofran birth defects. For example, a 2012 study found a 2.37 times greater risk for cleft palate, a birth defect wherein the front of the skull does not fully fuse together during pregnancy. This can usually be corrected surgically, though it can be a death sentence in situations wherein surgery is not an option for the child.

Despite these findings, the U.S. Food and Drug Administration recently rejected a petition to change Zofran’s drug category, saying in an October 2015 statement that these studies “do not support a determination that there is an increased risk of fetal adverse outcomes.”

Because of the risks Zofran birth defects may pose for both mother and child, many parents have chosen to file a Zofran birth defects lawsuit against the drug’s manufacturer.