A safe painkiller? New research raises concerns about Tylenol’s safety in pregnancy

Acetaminophen (often sold under the brand name Tylenol®, and known as paracetamol outside the United States and Canada) is the most commonly used over-the-counter pain and fever medication during pregnancy and is used by more than half of pregnant women worldwide. Until now, acetaminophen has been considered the safest option for managing headache, fever, and other pain. Analysis by the Mount Sinai-led team of 46 studies incorporating data from more than 100,000 participants across multiple countries challenges this perception and underscores the need for both caution and further study.

The Navigation Guide Systematic Review methodology is a gold-standard framework for synthesizing and evaluating environmental health data. This approach allows researchers to assess and rate each study's risk of bias, such as selective reporting of the outcomes or incomplete data, as well as the strength of the evidence and the quality of the studies individually and collectively.

"Our findings show that higher-quality studies are more likely to show a link between prenatal acetaminophen exposure and increased risks of autism and ADHD," said Diddier Prada, MD, PhD, Assistant Professor of Population Health Science and Policy, and Environmental Medicine and Climate Science, at the Icahn School of Medicine at Mount Sinai. "Given the widespread use of this medication, even a small increase in risk could have major public health implications."

The paper also explores biological mechanisms that could explain the association between acetaminophen use and these disorders. Acetaminophen is known to cross the placental barrier and may trigger oxidative stress, disrupt hormones, and cause epigenetic changes that interfere with fetal brain development.

While the study does not show that acetaminophen directly causes neurodevelopmental disorders, the research team's findings strengthen the evidence for a connection and raise concerns about current clinical practices.

The researchers call for cautious, time-limited use of acetaminophen during pregnancy under medical supervision; updated clinical guidelines to better balance the benefits and risks; and further research to confirm these findings and identify safer alternatives for managing pain and fever in expectant mothers.

"Pregnant women should not stop taking medication without consulting their doctors," Dr. Prada emphasized. "Untreated pain or fever can also harm the baby. Our study highlights the importance of discussing the safest approach with health care providers and considering non-drug options whenever possible."

With diagnoses of autism and ADHD increasing worldwide, these findings have significant implications for public health policy, clinical guidelines, and patient education. The study also highlights the urgent need for pharmaceutical innovation to provide safer alternatives for pregnant women.

The study was conducted in collaboration with the University of California, Los Angeles; University of Massachusetts Lowell; and Harvard T.H. Chan School of Public Health.

Funding for this study was provided by the National Cancer Institute (U54CA267776), the National Institute of Environmental Health Sciences (R35ES031688), and the National Institute on Aging (U01AG088684).