Harvard Study Links Prenatal Tylenol Use to Increased Risk of Autism, ADHD

Landmark Harvard Study Suggests Link Between Prenatal Acetaminophen and Neurodevelopmental Disorders

CAMBRIDGE, MA – A comprehensive systematic review led by researchers at the Harvard T.H. Chan School of Public Health has found evidence associating prenatal exposure to acetaminophen—the active ingredient in Tylenol and other pain relievers—with an increased risk of autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD) in children.

The study, published in BMC Environmental Health, analyzed data from 46 previous studies worldwide. Utilizing the rigorous "Navigation Guide" methodology, the analysis strengthens the evidence of a connection, particularly when acetaminophen is used for prolonged periods.

Key Findings and Researcher Recommendations

The research team, led by senior author Andrea Baccarelli, dean of the faculty at Harvard T.H. Chan School of Public Health, emphasized a nuanced approach.

• Strongest Association with Prolonged Use: The link to neurodevelopmental disorders (NDDs) was most significant when acetaminophen was taken for four weeks or longer during pregnancy.

• Risk-Benefit Balance is Crucial: The researchers caution against broad limitations, noting that acetaminophen remains a critical tool for managing fever and severe pain in pregnancy, both of which can themselves harm the fetus.

• Guidance for Use: They recommend "judicious acetaminophen use—lowest effective dose, shortest duration—under medical guidance."

FDA Echoes Caution for Clinicians

In line with these findings, the U.S. Food and Drug Administration (FDA) announced in late September that it would issue a letter urging healthcare providers to be cautious about prescribing acetaminophen during pregnancy. Dean Baccarelli confirmed that he had shared the study's conclusions with federal health officials prior to the FDA's announcement.

Conclusion and Further Research

The study concludes that while more research is needed to establish causality, the existing evidence warrants caution. "Based on existing evidence, I believe that caution about acetaminophen use during pregnancy—especially heavy or prolonged use—is warranted," Baccarelli stated.

The study was conducted in collaboration with the Icahn School of Medicine at Mount Sinai, UCLA, and the University of Massachusetts Lowell. Funding was provided by the National Institutes of Health.

--- This article is based on a press release from the Harvard T.H. Chan School of Public Health.