Tylenol’s active ingredient linked to language delay for baby girls

Pregnant women might want to watch their Tylenol use — girls born to mothers who used the pain reliever during pregnancy have higher rates of language delay, according to a new study.

The study is the first to examine mothers' use of Tylenol's active ingredient acetaminophen and babies' ability to learn and speak words at 2 ½ years old and suggests that the pain reliever—the most common drug ingredient in the U.S.—should be used sparingly during pregnancy.

"It's a very important finding, language delay at this age can predict a lot of problems for development and for later in life," said Nicki Bush, an associate professor of psychiatry and pediatrics at the University of California, San Francisco. Bush was not involved in the study.

The findings have big implications: There are more than 600 medicines that contain acetaminophen. Previous studies show almost everyone has acetaminophen in their system, even if they don't take it in medication. The industrial chemical aniline—found in everything from blue jeans to pesticides to personal care products—is converted to acetaminophen in people's livers.

However, pregnant women are more highly exposed—an estimated 65 percent of U.S. women take the drug while pregnant to relieve pain and fevers.

"Given the prevalence of prenatal [acetaminophen] use and the importance of language development, these findings, if replicated, would suggest that pregnant women should limit their use of this analgesic during pregnancy," the authors wrote in the study, published today in the journal European Psychiatry.

The study doesn't prove that acetaminophen spurs language delay in baby girls, however, it builds on previous studies linking the pain reliever to multiple health problems for babies, including altered hormones, reproductive disorders and asthma.

Scientists had 754 Swedish women report their acetaminophen use during pregnancy and tested their urine for the drug. When babies were 30-months old, parents and nurses reported on the baby boys' and girls' ability to speak, defining language delay as those that used fewer than 50 words.

A majority of the women, 59 percent, used the pain reliever. Girls born to mothers who used the drug heavily were almost six times as likely to have a language delay compared to girls whose mothers did not take the drug at all.

Though there were more language delays reported for boys, they didn't see the same association with the drug. "We found that surprising," said senior author of the study Shanna Swan, a professor of reproductive science at Mount Sinai Hospital in New York, who pointed out that previous studies of acetaminophen found more impacts on male reproduction than females.

Swan said it's not clear how the drug may influence a baby's language skills but it's possible that it is via an impact on hormones—specifically androgen, which acetaminophen has been shown to inhibit.

Bush said language delay at 2 ½ years old could spur a "downward spiral" of challenges, including difficulty reading and in school—which is linked to social challenges like rejection from peers, depression and anxiety over school problems, and bad behavior as a way of coping.

And this can all bleed into adulthood. "Educational attainments is linked to earnings, job satisfaction," Bush said.

Swan and colleagues didn't drill down on the reasons for language delay, which can be varied and include hearing or articulation problems, anxiety and autism.

The good news is "language delays have very good responses to early intervention," Bush said.

Researchers will follow the children in the study and check on their language development at 7 years old.

Johnson & Johnson, the parent company of Tylenol, did not respond to requests for comment.