Pregnant women who use Zofran should be aware of FDA warnings for life-threatening side effects like serotonin syndrome and irregular heart rhythm. Studies also suggest that Zofran may increase the risk of birth defects.

FDA Zofran Pregnancy Warnings

The FDA classifies Zofran as a “Pregnancy Category B” medication, meaning it is not approved or recommended for pregnant women because its risks to a developing baby are unknown.

The fetal safety data on Zofran is mostly based on animal studies conducted in the 1980s, which showed that Zofran crosses the placenta. In the last decade, several studies in humans have shown that Zofran rapidly passes to a developing baby in “significant amounts,” and remains active in the fetus longer than it does in a pregnant woman.

A number of recent studies have also suggested that Zofran could increase the risk of having a baby with a birth defect. One study involving 900,000 pregnancies in Denmark found a 30% increased risk of birth defects and a doubled risk of heart defects. Other studies have found that Zofran doubles the risk of cleft palate.

FDA Warning: Zofran and Abnormal Heart Rhythms

September 15, 2011 — The FDA issued a Safety Communication for Zofran to warn about the risk of abnormal changes in the electrical activity in the heart, which could lead to a potentially deadly abnormal heart rhythm.

The FDA did not specifically address the heart risks of Zofran in pregnant women because it is not approved during pregnancy.

However, pregnant women on Zofran may be even more likely to develop this side effect. Zofran is commonly used for the “off-label” (unapproved) treatment of severe morning sickness, also known as hyperemesis gravidarum. Extreme vomiting can also cause electrolyte imbalances that can lead to heart problems.

Heart risks of Zofran include:

  • Electrolyte imbalances
  • QT interval prolongation
  • Abnormal heart rhythm
  • Shortness of breath
  • Heart palpitations or fluttering
  • Torsades de pointes
  • Heart failure
  • Cardiac arrest
  • Death

FDA Recalls 32-mg Zofran Due to Heart Rhythm Concerns

June 29, 2012 — The FDA has issued a recall for 32-mg single intravenous (IV) doses of Zofran because it could predispose patients to develop abnormal heart rhythm disorders that could be deadly.

FDA Warning: Zofran and Serotonin Syndrome

March 2013 — The FDA has identified a potential safety issue linking Zofran and serotonin syndrome.

Zofran is a serotonin-3 (5-HT3) receptor antagonist, which means it works by selectively blocking serotonin signaling. The FDA is concerned that this could lead to serotonin syndrome, a life-threatening condition associated with increased serotonin signaling in the brain.

The risk in pregnant women was not addressed by the FDA, but up to 14% of pregnant women take antidepressants. The most popular antidepressants (SSRIs) work by influencing serotonin levels in the brain. It is possible that combining Zofran and antidepressants could adversely impact serotonin levels lead to severe complications.

Symptoms of serotonin syndrome:

  • Confusion
  • Agitation or restlessness
  • Dilated pupils
  • Headache
  • Changes in blood pressure and/or temperature
  • Nausea and/or vomiting
  • Diarrhea
  • Rapid heart rate
  • Loss of muscle coordination
  • Shivering
  • Sweating


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