NEW YORK - Expectant mothers often take Tylenol, with the active ingredient acetaminophen, to deal with back pain, headaches or mild fevers during pregnancy. But frequent use may be linked to poorer language skills and behavior problems among their children, according to a new study.
As the most popular over-the-counter drug in the U.S., Tylenol has been extensively studied in relation to premature birth and miscarriage, with no connections found.
But its maker Johnson & Johnson periodically comes under fire for the drug's small therapeutic index - that is, the difference between an effective dose and a dangerous dose is quite small. So interest in investigating the drug persists.
The new study is the first to look at young children whose mothers took Tylenol while pregnant.
"Our findings suggest that (acetaminophen) might not be as harmless as we think," Ragnhild Eek Brandlistuen said. She led the study at the School of Pharmacy at the University of Oslo in Norway.
She and her co-authors studied 48,000 Norwegian children whose mothers answered survey questions about their medication use at weeks 17 and 30 of pregnancy, and again six months after giving birth.
Mothers filled out a follow-up questionnaire about their child's developmental milestones three years later.
Close to 4 percent of women took Tylenol for at least 28 days total during pregnancy.
Their children seemed to have poorer motor skills than kids whose mothers had taken the drug fewer times or not at all. Tylenol-exposed kids also tended to start walking later, have poorer communication and language skills and more behavior problems.
It's difficult to define risks for pregnant women and their children, since rigorous tests and controlled studies of drug exposure aren't ethical, Brandlistuen said. All researchers can do is closely observe women in the real world.
But this study, published in the International Journal of Epidemiology, involved a large number of women, and researchers also looked for any link to ibuprofen, a pain-relief alternative without acetaminophen.
They found no development problems tied to ibuprofen.
"Long-term use of (acetaminophen) increased the risk of behavior problems by 70 percent at age three," Brandlistuen said. "That is considerable."
Heavy users most often reported taking the drug for five to seven days in a row a few times during pregnancy, she said.
"Sixty-five percent of women will take this drug at some point during pregnancy," Ann Z. Bauer said. She is a doctoral candidate at the School of Health and Environment at the University of Massachusetts Lowell.
Bauer was not involved in the new research but has studied Tylenol and autism risk.
"Some people just pop Tylenol when they have a headache," Dr. Martha Herbert, an autism researcher at Massachusetts General Hospital in Boston, said.
The developmental problems seen in this study align with symptoms of autism spectrum disorder, though the children had not been diagnosed at age three. Herbert has been studying the possible link between acetaminophen and the disorder for several years.
"I don't think it's a done deal," she told Reuters Health. She doesn't like to pin "the cause of autism" on any one thing, as many factors are likely involved.
"But for those people who wish to take precautions, this is something they can do," Herbert said, referring to pregnant women cutting down on Tylenol use or choosing ibuprofen instead.
"With every choice you make, make the healthy choice," she said.
In a statement to Reuters Health, Jodie Wertheim a spokesperson for Johnson & Johnson, said the drug "has an exceptional safety profile. As the authors note in the study, there are no prospective, randomized controlled studies demonstrating a causal link between acetaminophen use during pregnancy and adverse effects on child development."
Wertheim continued, "We always recommend that consumers carefully read and follow label instructions when using any over the counter medication. In addition, our label notes if pregnant or breast-feeding, ask a health professional before use. Consumers who have medical concerns or questions about acetaminophen should contact their health care professional."
The developmental effects Brandlistuen's team noted at age three could manifest differently or disappear with age, but only future studies can answer that question, she said.
"Since this is the only study to show this, there is a need for further research to confirm or refute these results before too many implications are made," she said.