Children of women who took acetaminophen, found in common over-the-counter medications such as Tylenol or Excedrin, were at a higher risk of developing attention deficit hyperactivity disorder or hyperkinetic disorder, which is very similar to ADHD but characterized by more severe impairments.
The research results were released Monday in the online edition of the JAMA Pediatrics, a publication of the American Medical Association. The study of more than 64,000 Danish children found that those whose mothers used acetaminophen were 37 percent more likely to have a hospital diagnosis of hyperkinetic disorder at or after turning 5, as well as 13 percent more likely to be exhibiting ADHD-like symptoms by age 7, and 29 percent more likely to be using ADHD medications.
The absolute risk of a child having ADHD-like symptoms by age 7 was relatively small, whether a mother took acetaminophen or not. The study found that about 2.5 percent of children had such symptoms if their mothers never reported taking the drug; the rate went up to about 3.4 percent if their mothers reported taking it at least once during a pregnancy.
The researchers found that acetaminophen use during pregnancy was widespread; more than half of the mothers in the study used the drug. The longer the women took acetaminophen, the stronger the correlation with the behavioral disorders—when women reported taking acetaminophen for more than 20 weeks during pregnancy, the risk to their children for hyperkinetic disorder nearly doubled, and the likelihood of their children taking ADHD medications increased by 50 percent.
The risk to children remained even after controlling for mothers who reported fever or inflammation during their pregnancies, or who reported use of other painkillers such as aspirin or ibuprofen.
The authors studied children and mothers in the Danish National Birth Cohort from 1996 to 2002. Mothers were asked three times during pregnancy, and once 6 months after the birth, about their use of painkillers. Around age 7, the mothers were contacted and asked to report any behavioral problems for their children on a questionnaire. Hyperkinetic disorder diagnoses and prescriptions for ADHD medications such as Ritalin were collected from Danish registries.
The researchers said that acetaminophen has been found to be an endocrine disruptor, and exposure to endocrine disruptors may affect neurodevelopment.
“We need further research to verify these findings, but if these results reflect causal associations, then acetaminophen should no longer be considered a ‘safe’ drug for use in pregnancy,” said Dr. Jørn Olsen, a senior author on the study and a former chairman of the epidemiology department of the Fielding School of Public Health at the University of California-Los Angeles. His comments were made in an article on the findings released by UCLA. The study was conducted by the University of Aarhus in Denmark in collaboration with the Fielding School.
A corresponding article published in JAMA Pediatrics along with the research results said that this study alone should not alter practice. “However, they underline the importance of not taking a drug’s safety during pregnancy for granted,” the editorial said.