The Tylenol-Autism Controversy Just Got Its Answer
A landmark Lancet review rebuts years of alarm over acetaminophen use in pregnancy — but the politics may take longer to settle.
A Decade of Fear Over Tylenol and Autism May Finally Be Ending
For more than a decade, headlines and social media posts warned that taking Tylenol during pregnancy might raise the risk of autism or ADHD in children. The idea that a common over-the-counter pain reliever used by millions could be neurologically harmful frightened expectant mothers. A new analysis in The Lancet Obstetrics, Gynaecology, and Women’s Health appears to close the case: the drug is not the culprit.
The study, published Friday, is the most comprehensive review of the question to date — pooling results from 43 cohort studies across Europe, North America, Japan, and Australia, representing millions of pregnancies.
Randomly assigning pregnant women to take or avoid a medication that might affect fetal development would violate basic research ethics, since withholding treatment could endanger those with high fevers or severe pain, while deliberately exposing others to a suspected risk would be equally indefensible. That’s why scientists must rely on large, carefully controlled observational studies, the closest ethical approximation to experimental proof.
But the study arrives in a charged political climate. The Department of Health and Human Services — whose leaders, including Secretary Robert F. Kennedy Jr., have previously claimed a link between Tylenol and autism — is standing by its more cautious position, citing an earlier 2025 Environmental Health paper that reached the opposite conclusion.
What the Science Shows
The Lancet team took another look at decades of research on acetaminophen, or “paracetamol,” and found that earlier warnings about risk didn’t hold up under closer study. Their big improvement was using sibling-comparison studies, which let researchers compare children born to the same parents — one exposed to Tylenol in the womb and one not. Because siblings share genes and grow up in the same home, this method helps rule out other factors that could explain differences, like family background or income. When the researchers did that, the supposed links between Tylenol and autism or ADHD disappeared.
This approach helps explain why the Lancet paper came to a very different conclusion than a 2025 study in Environmental Health, which had suggested a possible connection. That earlier review included many smaller, less reliable studies where mothers were asked to remember if and how much Tylenol they had taken months or even years earlier. This opens the door to what scientists call recall bias — when parents who have a child with a health condition are more likely to overestimate or misremember the mother’s medication use during pregnancy than those whose children are healthy. The Environmental Health study also didn’t fully account for why women took Tylenol in the first place — for example, to treat fever or infection, both of which can affect a baby’s brain development on their own.
The Lancet researchers focused instead on stronger studies that used medical or pharmacy records, adjusted for maternal illness, and controlled for genetics and home environment. Once those differences were taken into account, the apparent risk vanished.
That finding matches long-standing advice from the American College of Obstetricians and Gynecologists, the Royal College of Obstetricians and Gynaecologists, and the European Medicines Agency, all of which recommend acetaminophen as the safest first choice for fever or pain during pregnancy.
The Counterpoint
Not everyone agrees with the Lancet findings. Officials at the Department of Health and Human Services (HHS) say they are not changing their position. “[M]any experts have expressed concern of the use of acetaminophen during pregnancy, including Dr. Andrea Baccarelli,” said agency spokesperson Andrew Nixon in a statement. Dr. Baccarelli is the Dean of the Harvard School of Public Health and an author on the Environmental Health study..
Dr. Jay Bhattacharya, the Director of the National Institutes of Health, criticized the Lancet study for using sibling controls, writing on X that while sibling studies can control for shared genes and family environment, they also have weaknesses. They only include families with multiple children who had different exposures, which can limit sample size and introduce new forms of bias. “Families with discordant siblings aren’t random,” Bhattacharya wrote. “They may differ in ways that matter for the outcome. Sibling studies can ‘wash out’ real effects, making a true link look like nothing.” Bhattacharya did not address the other methodological differences between the two studies, including, importantly, whether they controlled for why a woman took Tylenol during pregnancy.
What Pregnant Women Should Know
For now, medical guidance remains unchanged: acetaminophen is safe when used as directed, including during pregnancy. Alternatives such as ibuprofen and aspirin carry well-documented pregnancy risks, including kidney damage and fetal heart complications. Leaving pain or high fever untreated can itself endanger both mother and baby.
Mothers wanting to reduce the risk of neurodevelopmental disorders in their baby should do what they can to prevent infections during pregnancy. This includes receiving all recommended vaccinations: Tdap, influenza, COVID, and RSV. Infections and fevers during pregnancy are known to increase the risk of neurodevelopmental disorders in the fetus.