A study in the November 2017 Pediatrics found long-term use of acetaminophen during pregnancy, as well as extended use of the common over-the-counter pain medicine by fathers, was associated with twice the risk of Attention Deficit Hyperactivity Disorder (ADHD) in children.

At the same time, the Norwegian study, "Prenatal Exposure to Acetaminophen and Risk of ADHD," which was published online Oct. 30, found short-term prenatal acetaminophen use of a week or less was associated with decreased rates of ADHD.

"Long-term acetaminophen use during pregnancy is related to more than a twofold increase in risk for offspring ADHD," after adjusting for genetic risk factors, indications for the mother's acetaminophen use, use of the drug before pregnancy, and other potential confounders, lead author Eivind Ystrom, PhD from the Norwegian Institute of Public Health, Oslo, and colleagues write in an article published online and in the November issue of Pediatrics.  Conversely, use of acetaminophen for less than 8 days during pregnancy was associated with a decrease in ADHD risk, suggesting its antipyretic effect "could be beneficial with regard to fetal development," the authors add.

The study does not provide definitive evidence for or against a causal relation between maternal use of acetaminophen, which is the recommended medication for pregnant women with fever or pain.  However, authors say the association they found calls for further study and more cautious consideration of its use during pregnancy.

For the study, researchers examined data from 112,973 children in the Norwegian Mother and Child Cohort Study, including 2,246 with an ADHD diagnosis. After adjusting for mothers' use of acetaminophen before pregnancy, family risk factors for ADHD, and other circumstances, researchers found prenatal acetaminophen use of less than 7 days was negatively associated with ADHD in children. 

For use lasting more than 7 days, the risk of children being diagnosed with ADHD increased with the number of days exposed; those who had 29 or more days of prenatal acetaminophen exposure were more than twice as likely to be diagnosed with ADHD. The data also showed children whose mothers took acetaminophen for fever and infections for 22 to 28 days were six times more likely to have ADHD. Among other findings, fathers who had taken acetaminophen for 29 or more days prior to conception had twice as many children with ADHD.