New research suggests taking acetaminophen during pregnancy could be linked to ADHD in offspring.

"The causes of ADHD and hyperkinetic disorder are not well understood, but both environmental and genetic factors clearly contribute," Doctor Beate Ritz, professor and chair of the department of epidemiology at the Fielding School and one of the senior authors of the paper, said in a UCLA  Fielding School  of Public Health news release. "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."

"That gave us the motivation to search for environmental causes that are avoidable," Doctor Jørn Olsen, another senior author and former chair of the UCLA Fielding School's epidemiology department, said in the news release. "Part of the neuropathology may already be present at birth, making exposures during pregnancy and/or infancy of particular interest. Because acetaminophen is the most commonly used medication for pain and fever during pregnancy, it was something we thought we should look at."

Researchers looked at 64,322 children and mothers who participated in a Danish cohort study. Telephone interviews were used to determine the mothers' acetaminophen use during pregnancy. The team followed up when the children were about seven years old. They asked the parents about any behavioral problems their children might have using the Strength and Difficulties Questionnaire. They also determined if the children had been diagnosed with hyperkinetic disorder.

Over half the mothers reported using acetaminophen while pregnant; these women's children were found to be between 13 and 37 percent more likely to be diagnosed with ADHD.

"It's known from animal data that acetaminophen is a hormone disruptor, and abnormal hormonal exposures in pregnancy may influence fetal brain development," Ritz said.