Studies Continue to Raise Red Flags on Tylenol Use During Pregnancy

New research out of Denmark is adding fuel to growing concerns about the safety of Tylenol's active ingredient during pregnancy, this time pointing to possible effects on reproductive development in baby girls.

A study from Copenhagen Analgesic found that girls exposed to paracetamol — the drug known as acetaminophen in the U.S. — while in the womb had smaller ovaries, fewer ovarian follicles, altered reproductive hormone levels, and reduced uterine size as infants.

Researchers followed 685 pregnant women in Denmark from early pregnancy and examined 302 of their healthy baby girls at three months old, tracking paracetamol exposure through biweekly self-reports and urine testing.

Despite the findings, study co-author Dr. Margit Bistrup Fischer stressed the results shouldn't cause panic. "Our study does not suggest that pregnant women should stop using paracetamol when it is genuinely needed, particularly for fever or significant pain," she said, though she noted it adds to a "growing signal" that pregnant women should be cautious with a drug often assumed to carry no risk.

Fischer emphasized that many daughters of mothers who used the drug showed ovarian measurements similar to those whose mothers didn't use it at all, and cautioned that the study can't predict outcomes for any individual child.

The American College of Obstetricians and Gynecologists urged caution in interpreting the findings, noting the study's participants were only followed into adolescence and cannot establish whether the differences translate into future fertility or reproductive health problems. The group also pointed to the study's observational design, which can't prove direct causation.

Still, the findings build on a troubling pattern. It was previously reported that Janssen, the pharmaceutical company behind Tylenol, privately acknowledged internal concerns linking prenatal acetaminophen use to neurodevelopmental conditions like autism years before the issue became public. In 2018, a company epidemiologist reportedly said "the weight of the evidence is starting to feel heavy."

The FDA issued a formal notice to physicians in September 2025 warning that mounting evidence suggests acetaminophen use during pregnancy may be associated with increased risk of neurological conditions like autism and ADHD, particularly with chronic use throughout pregnancy.

With up to 65% of American women reporting acetaminophen use at some point during pregnancy, experts say the growing body of research deserves serious attention from doctors, regulators, and expectant mothers alike.