The Truth About Taking Tylenol When You’re Pregnant by Sy Mukherjee @FortuneMagazine August 16, 2016, 1:49 PM EST E-mail Tweet Facebook Linkedin Share icons Acetaminophen is the most common drug ingredient in the United States, found in more than 600 medicines. Now a new study is raising alarm by suggesting using acetaminophen (the active painkilling ingredient in Tylenol) during pregnancy can lead to an increased risk of ADHD and behavioral problems in children. Scientists from the University of Bristol published their findings in the medical journal JAMA Pediatrics on Monday. They analyzed data taken from 7,800 U.K. mothers (and their partners and children) from pregnancy until the kids were seven-years-old. The researchers found that the children of mothers who had taken acetaminophen at 18 and 32 weeks of pregnancy were more likely to have behavioral problems and ADHD by the time they turned seven than those who hadn’t. (More than half of mothers in the study said they’d used acetaminophen at 18 weeks). There was a 42% increased risk for behavioral issues and 31% increased risk for hyperactivity in these children which didn’t show up in those whose mothers hadn’t taken the painkiller while pregnant. Click here to subscribe to our upcoming Brainstorm Health Daily Newsletter. But there’s plenty of nuance to the analysis, and researchers noted that abstaining from acetaminophen despite fever or pain “should be carefully weighed against any potential harm of acetaminophen to the offspring.” (Pregnant women are advised not to take aspirin.) For instance, the study authors didn’t ask how much or how frequently the women took acetaminophen. And the data suggest that factors such as whether or not the Tylenol-taking mothers also smoked or drank during pregnancy, or had a psychiatric condition, may well have played a role in the results, as NPR points out. It’s also important to note just what the elevated risk numbers mean. A 31% increased risk for ADHD sounds scary at first — but it represents a pretty modest rise in absolute terms. Just under 5% of all the children in the study showed signs of increased behavioral problems, with just a two percentage point difference between those whose mothers hadn’t taken acetaminophen and those who had. That’s why the researchers say that followup studies must be done to truly establish a cause-and-effect relationship (although some previous analyses pointed out similar links) and stressed that they aren’t recommending that pregnant women in pain ditch acetaminophen, which many medical professionals believe to be the safest painkiller to take during pregnancy. Acetaminophen has been scrutinized in a number of studies. Most recently, a May report from the Ohio State University suggested that people taking the drug may have a harder time feeling empathy for others.