pills spilling from a bottleNew research from the University of California – Los Angeles Fielding School of Public Health and the University of Aarhus in Denmark has found that over-the-counter painkiller acetaminophen can increase the risk of attention deficit hyperactivity disorder (ADHD) and hyperkinetic disorder (a more severe form of ADHD). The results demonstrated that women who took acetaminophen during pregnancy were more likely to have children with ADHD or hyperkinetic disorder.

The research team wanted to find environmental factors that could be contributing to the rapid rise of neurodevelopmental disorders like ADHD; specifically, they sought to identify avoidable causes of said disorders. Since acetaminophen is one of the most commonly used medications among pregnant women, they structured the study to evaluate the relationship between acetaminophen use during pregnancy and later indicators of ADHD or hyperkinetic disorder.

This study was comprised of data from several Danish long-term cohort studies. The researchers started with the Danish National Birth Cohort, a nationwide study of pregnancies and children. They winnowed the records to 64,322 children and mothers who were enrolled in the cohort from 1996 to 2002. Use of acetaminophen was determined through computer-assisted telephone interviews conducted up to three times throughout the pregnancy and once six months post-childbirth. When the children reached age seven, researchers followed up with parents regarding the children’s behavior using the Strength and Difficulties Questionnaire, a standard behavioral screening. Data also came from the Danish National Hospital Registry and the Danish Psychiatric Central Registry, which provided information about the children with hyperkinetic disorder. Finally, they used the Danish pharmaceutical prescription database to determine whether families redeemed ADHD medications such as Ritalin.

Acetaminophen use during pregnancy was associated with a higher risk of ADHD and of hyperkinetic disorder and it was associated with a 13% to 37% higher risk of later receiving a hospital diagnosis of hyperkinetic disorder, being treated for ADHD with medication, or having ADHD-like behaviors at age seven. The association between acetaminophen use and neurodevelopmental disorders was even stronger when pregnant women used it in the second and third trimesters. Moreover, there was a 50% greater risk for ADHD and hyperkinetic disorder when the mother used acetaminophen for more than 20 weeks of pregnancy.

This research is published online in JAMA Pediatrics.

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