Tylenol Use While Pregnant May Be Connected To Reproductive Changes In Young Girls, Study Suggests

Exposure to Tylenol’s active ingredient while in the womb may potentially impact reproductive organ development in young girls, according to a new study from across the Atlantic.

Copenhagen Analgesic’s (COPANA) study found that girls exposed to the drug paracetamol in utero had smaller ovaries, fewer ovarian follicles, differences in reproductive hormone levels and reduced uterine size during infancy.

The study enrolled 685 pregnant women in Denmark during the first trimester of pregnancy and examined 302 of their healthy infant girls when they were three months old.

Still, the researchers note that “whether these early-life differences have long-term clinical relevance, including effects on reproductive lifespan, remains uncertain” and requires further research with extended follow-up.

“Our study does not suggest that pregnant women should stop using paracetamol when it is genuinely needed, particularly for fever or significant pain,” study co-author Dr. Margit Bistrup Fischer told the Daily Caller News Foundation. “However, it does contribute to a growing signal that we should pay closer attention to use during pregnancy, especially because paracetamol is an over-the-counter medicine that is often perceived as entirely risk-free.”

The drug is known as acetaminophen in the U.S. Japan, and paracetamol in Denmark, the rest of Europe and most other countries. In addition to it being the primary active ingredient in Tylenol products, it is also among the most common active drugs nationwide, according to the company’s website.

“We hope this study will stimulate further research in this area as well as discussions among researchers, clinicians, and regulatory authorities,” Fischer continued. “While our findings add to a growing body of evidence, there is a need for larger studies with longer follow-up to determine whether the associations we observed with markers of female reproductive development and ovarian reserve translate into differences in reproductive health later in life.”

Researchers assessed paracetamol exposure using pregnant women’s reports of paracetamol use collected bi-weekly and by measuring paracetamol in their urine samples, according to the report.

Fischer also emphasized that any “women who have used paracetamol during pregnancy should not be alarmed” by the study’s findings.

“Our study examined associations at the population level and cannot predict outcomes for any individual woman or child,” she explained. “Many women who used paracetamol during pregnancy had daughters whose ovarian measurements were similar to those of daughters born to women who did not use paracetamol. Paracetamol remains an important treatment option during pregnancy, particularly for conditions such as high fever or significant pain, where treatment may be important for both maternal and fetal health.”

“This is the first human study specifically designed to investigate whether prenatal paracetamol exposure is associated with markers of ovarian development in daughters,” according to the report.

The researchers also note that while the study “cannot prove that paracetamol directly caused these differences, the findings are consistent with results from animal studies.”

Multiple experimental animal studies have suggested that offspring of mothers given the drug while pregnant had smaller ovaries and fewer eggs, CNN reported.

“While this study reports associations between prenatal acetaminophen exposure and certain measures of ovarian and uterine development in offspring, as the authors themselves state, the clinical significance of these findings is uncertain or unknown,” an American College of Obstetricians and Gynecologists (ACOG) spokesperson told the DCNF in a statement. “The oldest participants evaluated were adolescents, and the study cannot determine whether the observed differences are associated with future reproductive outcomes such as fertility, ovulatory function, reproductive lifespan, or other measures of reproductive health.”

“The authors also acknowledge important limitations, including substantial inter-individual variability in these measures and the inability to establish causality from an observational study,” the ACOG spokesperson added.

Up to 65% of U.S. women report taking paracetamol at some point during their pregnancy, according to Harvard Health.

However, Janssen, the pharmaceutical company that makes Tylenol, privately acknowledged the potential connection between prenatal use of the drug and neurodevelopmental conditions like autism in children several years ago, the DCNF first reported in September 2025.

“The weight of the evidence is starting to feel heavy to me,” Rachel Weinstein, U.S. director of epidemiology for Janssen, the pharmaceutical arm of Johnson & Johnson, said in 2018, the DCNF reported.

The U.S. Food and Drug Administration (FDA) issued a notice to physicians regarding the use of the active Tylenol ingredient during pregnancy on Sept. 22, 2025, claiming that “in recent years, evidence has accumulated suggesting that the use of acetaminophen by pregnant women may be associated with an increased risk of neurological conditions such as autism and ADHD in children.”

“Some studies have described that the risk may be most pronounced when acetaminophen is taken chronically throughout pregnancy to childbirth,” according to the FDA’s letter. “These concerns may be magnified by the fact that a very young child’s liver may still be developing and thus a child’s ability to metabolize the drug may be limited.”