Now more than ever, science knows how to carry a pregnancy safely to term. Exercise is good; smoking and drinking is bad — among other warnings. But as pharmaceutical fixes to common ailments become more prominent, gray areas emerge. A recent study has found that mothers who use Tylenol for fever reduction while pregnant reported greater ADHD-like symptoms in their children.

The problem is, the main ingredient in Tylenol, acetaminophen, isn’t necessarily dangerous. Leaving a fever untreated, in fact, could pose even greater harm to a baby’s development than taking a drug to alleviate the symptoms. The Food and Drug Administration (FDA) draws lines in the sand when it comes to these pregnancy-related drug concerns, and as it turns out, acetaminophen may be the least of a mother’s worries.

To Treat or Not to Treat?

Researchers from several international universities collected data on 64,000 Danish mothers and children. They learned how often and at what point in gestation mothers took Tylenol, or related acetaminophen-releasing medication, to treat fevers. To preserve their true intentions, the team collected this data far before mothers had the chance to report any ADHD symptoms, lest their memories taint in favor of what they’re being asked to recall. Ultimately, the scientists found that acetaminophen use in the last two trimesters of pregnancy yielded a 63 percent greater risk for ADHD symptoms. In the third trimester alone, the risk fell to 28 percent. And in just the first trimester, it was only 9 percent.

"The causes of ADHD … are not well understood, but both environmental and genetic factors clearly contribute," said Dr. Beate Ritz, professor in UCLA’s department of epidemiology and one of the senior authors, in a statement. "We know there has been a rapid increase in childhood neurodevelopmental disorders, including ADHD, over the past decades, and it's likely that the rise is not solely attributable to better diagnoses or parental awareness. It's likely there are environmental components as well."

So the team sought to understand how certain controllable components may factor into fetal development. They already knew, for example, that acetaminophen can cross the placental barrier and enter the growing fetus’s brain. As a tested hormone disruptor, it may be the case that Tylenol’s main ingredient interferes with proper hormone balances in utero, preventing the otherwise normal development from taking place.

This raises the question, though, of what mothers can do if they’re experiencing pain or feel a fever coming on. For that, the FDA steps in. Among its many duties, the agency has control over classifying the safety of certain drugs during pregnancy — a set of labels known as the Pregnancy Risk Categories. They include A, B, C, D, X, and N. Categories A-D move from the safest drugs to the ones most likely to cause problems. Category X drugs are entirely unsafe and shouldn’t be consumed while pregnant under any circumstances. The final category, N, includes drugs on whom no testing has yet been done, so the agency can’t offer a suggestion one way or another.

“B” Healthy

Where does acetaminophen fit in? The agency pegs it at a B. Meanwhile, ibuprofen, another common pain reliever, receives a D. Neither medicine should be taken heavily, if at all during the third trimester, as the complications they could produce aren’t as easily treated than if they were found earlier on in gestation.

While the FDA classifies a B drug as one that hasn’t been shown “to demonstrate a risk to the fetus” in “adequate and well-controlled studies in pregnant women,” the present study argues acetaminophen poses just such a risk. "We need further research to verify these findings, but if these results reflect causal associations, then acetaminophen should no longer be considered a 'safe' drug for use in pregnancy,” said University of Aarhus' Dr. Jørn Olsen, another senior author, in the release.

Ideally, the debate over Tylenol use is squashed from the outset if a woman stays healthy all throughout her pregnancy. She can accomplish this through regular light to moderate exercise and a healthy diet, rich in lean proteins and vegetables, in order to keep both her and her baby’s immune system strong. In a related editorial to the study, a collection of British experts on ADHD argued that physicians and pregnant women shouldn’t change their behavior as it applies to Tylenol usage, primarily because the dosages involved in the study were left unclear.

UCLA obstetrician Dr. Daniel Kahn echoed the trio’s comments, as he argues that when prevention efforts fail, the non-treatment route is rarely the safer bet compared to medicating an illness. “This highlights the point that the lowest exposure is always the best, for any agent,” Kahn told the Los Angeles Times. Pregnant women should “use as little as possible to meet your needs, and if you’re having unmet needs beyond that, we need to talk about it.”

Source: Liew Z, Ritz B, Rebordosa C, Chen Lee-P, Olsen J. Acetaminophen Use During Pregnancy, Behavioral Problems, and Hyperkinetic Disorders. JAMA Pediatrics. 2014.