Tylenol During Pregnancy Linked to Higher Risk of ADHD

Pregnancy is already a fraught time for expectant moms, as more research shows how quickly the foods that women eat, the air they breathe and the compounds to which they are exposed can traverse the placenta and affect their growing child. Now there’s another thing to add to the growing list of agents — including tobacco from cigarettes, mercury from fish, and alcohol — that may affect their babies’ development.

In a study published in JAMA Pediatrics, an international group of researchers led by Dr. Jorn Olsen, at the University of Aarhus, in Denmark, found a strong correlation between acetaminophen (found in common painkillers like Tylenol) use among pregnant women and the rate of attention-deficit/hyperactivity disorder (ADHD) diagnoses and prescriptions for ADHD medications in their children. Overall, moms who used the pain reliever to treat things like headaches or to reduce fevers saw a 37% increased risk in their kids receiving an ADHD diagnosis and a 29% increased risk in the chances that their kids needed ADHD medications compared with moms who didn’t use the over-the-counter medication at all.

(MORE: Majority of Doctors Do Not Follow Treatment Guidelines for ADHD)

Even after the team accounted for factors that could explain the connection, like why the mom needed to take the drug in the first place, the link remained strong, suggesting that there is something specific about the drug, and how it affects fetal development, that might explain the higher risk of behavioral issues.

The findings are especially troubling since more than half of the 64,322 women in the study reported using acetaminophen in the three months prior to the survey. The participants included mothers and singleton children born in Denmark between 1996 and 2002 and registered in the Danish National Birth Cohort, so it included a diverse group of mothers from different social and environmental backgrounds. The study also evaluated hyperactivity on three different levels — from symptom reports by mothers or caregivers, hospital diagnoses and prescriptions to treat ADHD. Higher acetaminophen use among mothers was linked to higher rates of all three outcomes in their children.

(MORE: Men Diagnosed With Childhood ADHD Struggle More With Jobs, Relationships)

“[The results] are worrisome because more than 50% of the women took acetaminophen; it’s an over-the-counter drug and they can freely buy, and use it at their discretion,” says Dr. Beate Ritz, one of the co-authors and chair of the Department of Epidemiology at the UCLA Fielding School of Public Health. “It’s considered relatively safe, and maybe it’s not.”

Previous studies have raised concerns about acetaminophen; both animal and human works have shown that the drug can interfere with hormone systems, so prenatal exposure may adversely affect development of the brain. Some studies showed the drug hampers the ability of the testes to descend during development as well. “Pregnancy is a very special period,” says Ritz. “Acetaminophen may not harm adults in any other way, but fetal development is special.”

(MORE: New ADHD Guidelines Include Kids as Young as 4)

The latest investigations from the neuroscientists studying developmental and behavioral disorders like autism and ADHD suggest that problems in the connection between different brain regions may contribute to the symptoms of these conditions, and hormone disruptions in utero, triggered by acetaminophen, may unbalance the brain enough to make certain children more vulnerable to autism or hyperactivity later in life.

The results are likely to launch waves of questions about how safe the drug is for pregnant women to take. Kate Langley, a lecturer in the School of Psychology at Cardiff University, in Wales, who wrote an accompanying editorial for the study, cautions that the findings only suggest an association, and do not establish that acetaminophen causes ADHD. “This is an interesting research paper, but it is way too early for it to inform our clinical practice at the moment,” she says.

Some women have a medical need to take acetaminophen, and they should continue to talk to their doctors about this latest risk. But for those who turn to the over-the-counter remedy for less medically urgent needs, such as relieving a headache or the pain of sore muscles, they should have a different kind of discussion with their doctors about the possible risks that the drug poses for their unborn child.

(MORE: Common Painkiller Use May Be Linked to Miscarriage Risk)

Ritz says more studies are needed using different sets of data to confirm and replicate what she and her colleagues found. But she appreciates how difficult it might be for expectant moms, or women who plan on having children soon, to wait for those studies to be completed. “As a scientist, I never want to be alarmist and use one study [to make clinical decisions],” she says. “But as a woman, when I see something like that, I would be worried, and wouldn’t take Tylenol during pregnancy any more.”

She says that women who need to take a pain reliever or need to control their fever should consider other alternatives, such as getting more rest or even gritting through the episode if they are especially worried about what their developing child might be exposed to. If more studies verify the potential harms on developing brains, it might also fall to regulatory agencies like the Food and Drug Administration to rethink the label of acetaminophen and warn users to avoid the medication during pregnancy.