Researchers at the Hebrew University of Jerusalem have for the first time found a link between the use of acetaminophen during pregnancy and an increased risk of autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD).

Acetaminophen (paracetamol or Tylenol) is one of the most common medications for treatment of pain and fever during pregnancy and has been considered safe in humans. However, evidence of neuro-disruptive properties is accumulating. Past studies have shown that long-term administration of low doses of acetaminophen may affect the development of the fetal nervous system and that this effect is often seen years after exposure during childhood.

In a first-of-its-kind meta-analysis, Dr. Ilan Matok at the Institute for Drug Research in Hebrew University’s Medical Faculty’s School of Pharmacy and doctoral student Reem Masarwa assessed the possible association between prolonged exposure to acetaminophen during pregnancy and the risk ADHD and ASD. Dr. Amichai Perlman and Dr. Hagai Levine of Hebrew University and the Hadassah University Medical Center also participated in the research.

Their recently published analysis in the American Journal of Epidemiology shows that prolonged exposure to acetaminophen during pregnancy is associated with a 30% increase in relative risk for ADHD compared to those who did not take acetaminophen during pregnancy and a 20% increase in relative risk for ASD.

Yet, given the significant limitations of existing studies, the researchers believe the results should be interpreted with caution, as they may cause unnecessary anxiety among pregnant women. It is important to understand that pain and fever during pregnancy can have a detrimental effect on the developing fetus, and that acetaminophen is still considered a safe drug for use during pregnancy. Therefore, if a pregnant woman has fever or pain, acetaminophen can be taken for a short period. If the fever or pain continue beyond that, she should consult her physician regarding further treatment.

The research covered 132,738 mother-child pairs with a follow- up period of three to 11 years.

“The findings suggest an association between prolonged acetaminophen use and an increase in the risk of autism and ADHD,” said Matok. “But the observed increase in risk was small, and the existing studies have significant limitations... We believe our findings should not alter current practice and women should not avoid use of short-term acetaminophen when clinically needed.”