Experts have gone back and forth on whether acetaminophen, found in Tylenol and a lot of other over-the-counter medicines, is safe to take during pregnancy. After a 2014 Danish epidemiological study concluded that women who reported taking acetaminophen during pregnancy were also more likely to report their child had attention deficit hyperactivity disorder-like behavior, a lot of headlines warned against frequent prenatal use of the drug. But not all experts agreed that the study proved a definitive link.
Now, there’s another large study published in the journal Pediatrics that backs up the findings of the 2014 report warning moms to proceed with caution when it comes to consuming the pain reliever. A group of researchers from Norway looked at 100,000 pregnancies and confirmed there is an association with extensive use of acetaminophen—defined as 29 consecutive days or more—and ADHD in children. This was a follow-up to a similar, smaller study the group had done in 2013 (different from the 2014 study mentioned above) that found children exposed to the drug had “poorer gross motor development, confidence interval, communication, externalizing behavior, internalizing behavior, and higher activity levels” than their unexposed siblings. (Kind of confusing, we know; basically three separate studies have confirmed the association.)
The New York Times, which has reported on the subject in depth, talked to Eivind Ystrom, a professor of psychology at the University of Oslo and a senior researcher at the Norwegian Institute of Public Health who worked on both studies, and is the lead author of the new article. He explained that he and the other researchers had always been skeptical of the first study’s results. So this time around, “We expected to find nothing,” he said.
This time they had better access to information about the mothers—including whether either parent had ADHD symptoms, since it’s highly hereditary, as well as information about other drugs the mother had taken and her symptoms during pregnancy—which allowed them to factor out certain health information. They then linked participants with the Norwegian patient registry to see which children were later diagnosed with ADHD. And still, even after adjusting for all the variables, the results remained the same.
“What we found was that regardless of the reason they used acetaminophen, those who reported long-term exposure — 29 consecutive days or more — had a more than twofold risk of ADHD,” Ystrom told the paper.
And, because the link was there for women who took the acetaminophen for different medical conditions, it appears less likely that it was an existing condition that was affecting the developing fetus in a way that later resulted in an ADHD diagnosis.
“We really tried all the tricks in the book to remove this effect and we can’t make it go away,” Ystrom said. “It’s a problem because it’s a recommended drug for pregnant women.”
Which is why he notes that this study still does not prove a cause-and-effect relationship between acetaminophen and ADHD. “Maybe those who used it for a very long time had more severe fever or more severe pain than those who didn’t use it,” he said. “That is the alternative explanation, that these mothers who used it for a long time, they had a more severe type of condition.”
The bottom line, like always, is to talk to your doctor. Researchers stress that long-term use is really the only concern here. In fact, women in the study who used acetaminophen for less than seven days of the pregnancy saw the risk of their child eventually being diagnosed with ADHD go down, which they haven’t been able to explain.
“Most pregnancies, short-term use is the only relevant use,” Ystrom said. “Our worry is that those who need to take the drug when they have fever don’t do it; that would be really bad.”