DENMARK — A study of more than 1.5 million Danish children published Monday in JAMA Pediatrics found that taking acetaminophen during pregnancy had no effect on later autism diagnoses. The research adds to a body of evidence examining whether the common pain reliever, sold under the brand name Tylenol, poses developmental risks to children exposed to it in utero.

Researchers used Denmark's national health registry to track children born between 1997 and 2022. Of those children, 31,098 were exposed to acetaminophen in utero. Autism was diagnosed in 1.8% of children who were exposed to the drug before birth and in 3% of children who were not exposed, according to the study.

The findings follow mixed results from earlier research. A 2024 study in Sweden found a marginal link between prenatal acetaminophen exposure and autism that disappeared after accounting for siblings, suggesting a strong genetic component in autism. A 2025 review of existing studies in the United States found a potential relationship between acetaminophen use during pregnancy and autism but did not determine whether confounding factors were responsible.

In September 2025, health officials announced that the U.S. Food and Drug Administration would initiate a label change for acetaminophen to warn of a potential link to autism. President Donald Trump said at the time, "If you're pregnant, don't take Tylenol." He added, "Don't take Tylenol. Don't have your baby take Tylenol." Trump also said, "That's, for instance, in cases of extremely high fever that you feel you can't tough it out."

After the FDA announcement, orders for acetaminophen for pregnant women in emergency departments dropped by 16% during the initial study period, according to a separate study published in The Lancet. Three weeks after the announcement, the rate of acetaminophen orders for pregnant women dropped by as much as 20% before drifting to a 10% reduction, according to the Lancet study. There was no change in acetaminophen order rates among non-pregnant women of the same age following the announcement.

Orders for intravenously administered fluids and opioids for pregnant women did not decline following the announcement, according to the Lancet study, and doctors' orders for opioids did not increase during the study period in emergency departments. Jeremy Faust, an emergency physician at Mass General Brigham and a health services researcher at Harvard Medical School, was a co-author of the Lancet study.

Non-steroidal anti-inflammatory drugs such as ibuprofen, Aleve, or Motrin are usually not recommended during pregnancy because of bleeding risks and potential placenta issues, leaving acetaminophen as one of the few over-the-counter pain relief options available to pregnant women.