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Acetaminophen Use during Pregnancy Linked to ADHD

Acetaminophen provides many people with relief from headaches and sore muscles, and when used appropriately, it is considered mostly harmless. Over recent decades, the drug has become the medication most-commonly used by pregnant women for fevers and pain. But a study by UCLA, in collaboration with the University of Aarhus in Denmark, has raised concerns about acetaminophen’s risks during pregnancy.

  Ninety-one thousand dots represent every pregnant woman who enrolled in the Danish National Birth Cohort from 1996-2002 across the map of Denmark.
Graphic: Thomas Becker/University of Aarhus

The UCLA researchers show that taking acetaminophen during pregnancy is associated with a higher risk in children of attention-deficit/hyperactivity disorder (ADHD) and hyperkinetic disorder.

“The causes of ADHD and hyperkinetic disorder are not well understood, but both environmental and genetic factors clearly contribute,” says Beate R. Ritz, MD, PhD, chair of epidemiology at the UCLA Jonathan and Karin Fielding School of Public Health. “We know there has been a rapid increase in childhood neurodevelopmental disorders, including ADHD, over the past decades; it is likely there are environmental components.” The UCLA researchers used the Danish National Birth Cohort, a nationwide study of pregnancies and children, to examine pregnancy complications and diseases in offspring as a function of factors operating in early life. The cohort focuses especially on the side effects of medications and infections.

They studied 64,322 children and mothers who were enrolled in the cohort from 1996 to 2002. Acetaminophen use during pregnancy was determined, using computer-assisted telephone interviews that were conducted up to three times during pregnancy and again six months after childbirth. They also obtained diagnoses of hyperkinetic disorder among the cohort’s children and identified if ADHD medications had been obtained for the children.

More than half of the mothers reported using acetaminophen while pregnant; the children of those mothers were at a 13-percentto- 37-percent higher risk of later receiving a diagnosis of hyperkinetic disorder, being treated with ADHD medications or having ADHD-like behaviors at age 7. The longer acetaminophen was taken — that is, into the second and third trimesters — the stronger the associations. The risks for hyperkinetic disorder/ADHD in children were elevated 50 percent or more when the mothers had used the common painkiller for more than 20 weeks in pregnancy.

“It’s known from animal data that acetaminophen is a hormone disruptor, and abnormal hormonal exposures in pregnancy may influence fetal brain development,” Dr. Ritz says. She noted that acetaminophen can cross the placental barrier and suggested it is plausible that acetaminophen may interrupt fetal-brain development by interfering with maternal hormones or through neurotoxicity.

If further studies verify the findings, then acetaminophen should no longer be considered “safe” to use during pregnancy, the researchers say.

“Acetaminophen Use During Pregnancy, Behavioral Problems, and Hyperkinetic Disorders,” JAMA Pediatrics, 2014


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