CNN said Trump's Tylenol warning went against decades of evidence.
Now a new study out of Denmark is raising the same alarm, with real anatomical data behind it.
Researchers just found something different about baby girls whose mothers took the drug.
A Danish Hospital Just Ran the Tylenol Pregnancy Study No One Had Done Before
Researchers at Copenhagen University Hospital just finished the first human study built specifically to test something scientists had only seen in animals and lab dishes before now.
The COPANA study followed 685 healthy, pregnant women through their first trimester between March 2020 and November 2022.
Of those pregnancies, 302 baby girls were examined afterward.
The question was simple.
Does acetaminophen, the active ingredient in Tylenol, change how a baby girl's reproductive organs develop in the womb?
Acetaminophen is the pain reliever doctors have told pregnant women is safe for decades, the default answer whenever a fever or headache shows up.
Smaller Ovaries, Smaller Uteruses, and Fewer Egg-Holding Follicles
The answer, according to the study authors, is yes.
Girls whose mothers took acetaminophen early in pregnancy were born with smaller ovaries and smaller uteruses.
Girls exposed later in pregnancy had fewer ovarian follicles, the tiny structures that hold a woman's lifetime supply of eggs.
CNN put real numbers on it: 40 percent smaller ovarian volume, 13 percent smaller uterine volume, and 23 percent fewer follicles compared to girls whose mothers skipped the drug.
Exposed girls also had lower levels of a hormone called AMH, the same hormone doctors use to estimate how many eggs a woman has left.
A second group of 1,210 girls, tracked from infancy into adolescence as part of the separate Copenhagen Mother-Child Cohort, showed the same pattern.
Smaller ovaries in adolescence.
Smaller uteruses at puberty.
Scientists Warned About Acetaminophen and Fertility a Decade Before Anyone Listened
This wasn't a total surprise to researchers.
Years earlier, a lab study on human fetal ovary tissue found that acetaminophen interfered with ovarian development in a dish, long before anyone confirmed it in an actual pregnancy.
Researchers think the mechanism may run through hormones, since acetaminophen can suppress natural hormone signals in a developing fetus, an anti-androgenic effect scientists have documented in lab settings for over a decade.
Last year, Harvard researchers reviewed 46 separate studies and found a real, if still unproven, association between prenatal acetaminophen use and autism and ADHD.
"That association is strongest when acetaminophen is taken for four weeks or longer," the Harvard researchers found.
Mount Sinai researchers reported a similar pattern.
A large Lancet review this past January complicated that part of the story, finding no clear link between the drug and autism or ADHD at all.
But autism and ADHD are diagnosed years later from a symptom checklist, tangled up with genetics and a dozen other variables no one can fully sort out.
Ovarian volume and follicle counts get measured directly, on an ultrasound, the same day a doctor looks for them.
That's a different kind of evidence, and it's why the Danish findings are harder to wave away.
Trump and Kennedy Already Flagged This Pregnancy Drug Last September
Washington had already picked this fight before Copenhagen published a word.
Last September, Health Secretary Robert F. Kennedy Jr. announced the FDA would issue a physician notice and start the process of changing acetaminophen's safety label.
"We are also sharing new information about the potential risks of acetaminophen so patients can make a more informed decision," FDA Commissioner Marty Makary said at the time.
Tylenol's manufacturer, Kenvue, pushed back hard, insisting decades of use prove the drug is safe.
The American College of Obstetricians and Gynecologists rushed out a statement defending the drug almost immediately.
Plenty of mainstream outlets called the warning unproven too.
A Danish hospital just handed that fight a new set of numbers to argue over.
Even the Researchers Say Pregnant Women Deserve to Know This
The study's authors say so directly: none of this proves acetaminophen alone causes any of it, only that it matches what the animal studies already showed.
Longer follow-up and bigger studies are still needed before anyone knows whether these differences affect a woman's fertility down the road.
Pregnant women don't have many other options when a fever turns dangerous, since the alternatives carry well-documented risks too.
Dr. Margit Bistrup Fischer, the researcher who led the COPANA study, told CNN this is "something we need as a society to talk about and inform pregnant women more about, so they can make an informed decision."
That's a modest ask.
It still took a fight with Washington, a Danish hospital, and a public feud with the manufacturer just to get anyone talking about it at all.
Until then, the advice most pregnant women got was simply to take the pills and not ask questions.
Sources:
- Kelli Keane, "Study of Prenatal Tylenol Exposure Suggests Reproductive Organ Changes in Girls," Live Action News, 2026.
- Margit Bistrup Fischer et al., "Fetal Exposure to Paracetamol Is Associated With Altered Markers of Ovarian Development and Reduced Uterine Volume in Girls: The COPANA Study," Human Reproduction Open, 2026.
- U.S. Department of Health and Human Services, "HHS, Trump, Kennedy Announce Bold Actions to Tackle Autism Epidemic," HHS.gov, September 2025.
- Harvard T.H. Chan School of Public Health, "Using Acetaminophen During Pregnancy May Increase Children's Autism and ADHD Risk," Harvard T.H. Chan School of Public Health, 2025.
