The XX Factor

That New Study On Pregnant Women and Tylenol Isn’t Worth Worrying About—Yet

Acetaminophen, the main ingredient in Tylenol, is currently the only painkiller approved for pregnant women.

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A new study published in JAMA Pediatrics reports that children born to women who took acetaminophen, the main ingredient in Tylenol, during pregnancy might have a marginally higher risk of behavioral problems later in life. While findings like these will hopefully inspire further research into the potential side effects of what is currently the only painkiller available for pregnant women, they shouldn’t be cause for anyone to stop taking the drug altogether.

Researchers at the University of Bristol studied acetaminophen use during pregnancy in nearly 7,800 women and then followed up with these women seven years later. At that point, they had the moms fill out a questionnaire about their children’s behavior. They found women who took the drug during their 18th or 32nd week of pregnancy were 42 percent more likely to report hyperactivity and 31 percent more likely to report conduct problems than those who didn’t. Those who took it at 32 weeks were also 29 percent more likely to report emotional difficulties in their children.

This data might sound a little scary, persuasive even, but there are a number important caveats to keep in mind. The first is that pregnant women were “not asked detailed questions on dose or duration or indications of use.” This means that that these numbers don’t tell us the difference between a women who took the drug three times a day and a woman who took them three times a month. If acetaminophen can, in fact, cause behavioral issues, then such a distinction is important to clarify and, ideally, quantify.

Also, as NPR’s Richard Harris points out, the risk isn’t quite as high as those percentages might suggest. Harris dug into the supplementary data tables provided with the study and discovered that the increased risk is actually quite small. For example: “Among women who had not taken the drug, 4.3 percent of their children registered an elevated score on the ‘SDQ total difficulties’ test. Compare that with 6.3 percent of children born to women who did take the drug. … So, the risk went from a small percentage to a slightly less small percentage of these children,” he writes.

Harris notes that because the increase is relatively small, there lies the possibility that it is the result of a statistical fluke rather than the effects of the medicine. Also, the risk of taking acetaminophen faded, and sometimes disappeared, when adjusted for smoking, drinking, and psychiatric problems among the mothers.

Dr. Evie Stergiakouli, the study’s lead author, agrees that there is not enough to go on here to justify adding acetaminophen to the very long list of drugs women can’t take during pregnancy. “This does not mean it is not safe during pregnancy,” Stergiakouli told ABC. The American Congress of Obstetricians and Gynecology has said the same.

Previous studies have also found a connection between acetaminophen and behavioral issues, but they too were designed in a manner that makes it difficult to draw conclusions. The main issue with those studies, as Emily Oster points out at FiveThirtyEight, is that they didn’t take into account why these women were taking the drug in the first place. Therefore, the studies don’t tell us whether it was the condition behind the pain, and not the treatment of the pain, that was making the difference.

But even though the findings from the recent study, along with the previous ones, are inconclusive, they shouldn’t be ignored. Instead, they’re a useful reminder of how little we know about how different drugs affect pregnant women and serve as a call for more research. “Pregnant women may be the most underrepresented group in the entire clinical research process,” a 2011 report by the National Institutes of Health’s Office of Research on Women’s Health stated. Also, a 2013 study found that only 1 percent of industry-sponsored clinical trials during the course of one year were designed specifically for pregnant women and 95 percent excluded them.

As ProPublica’s Nina Martin points out in her story on this subject, the reason why there is so little research is likely “a deep-rooted cultural bias that elevates the fetus above all else.” And despite recent attempts by Food and Drug Administration to encourage research, “widespread aversion to prenatal research persisted.”

Still, there’s hope. Both the Senate and the House of Representatives are considering bills to establish a task force on research of pregnant and lactating women. The Senate’s proposed group would “provide advice and guidance to the Secretary [of Health and Human Services] regarding Federal activities related to identifying and addressing gaps in knowledge and research regarding safe and effective therapies for pregnant women and lactating women, including the development of such therapies and the collaboration on and coordination of such activities.” Pregnant women could really use that.