Researchers in Norway found that among almost 113,000 children, those whose mothers used acetaminophen during pregnancy were slightly more likely to be diagnosed with attention deficit hyperactivity disorder (ADHD).
Using the drug during just one trimester was associated with 7 percent higher odds of having a child with ADHD, while the increased risk was 22 percent for women who used acetaminophen in two trimesters and 27 percent with use in all three trimesters, the study found.
The same study also found a slightly decreased risk of ADHD in children whose mothers took the drug for seven days or less. "We were furthermore able to analyze maternal use of acetaminophen prior to pregnancy as a specificity control and to estimate the effect of paternal use prior to pregnancy".
Doctors generally advise pregnant women to take acetaminophen in the smallest dose possible for the shortest possible period of time when they have fevers.
"The last thing we'd want, heading into flu season, is for women not to use acetaminophen to get a fever down", she said. "It is important to pursue further research on the possible drug associations with the development of ADHD, and that research will require longitudinal follow-up of large numbers of children with and without ADHD", he wrote.
The lead author of the new study said pregnant women who are using the medicine for fever or pain relief "should not refrain from short-term acetaminophen use".
This isn't the first study to suggest a link between acetaminophen and ADHD, but some experts said the data don't support the findings and believe there are other factors are work.
Overall, researchers estimated that about 4 percent of the children in the study would have an ADHD diagnosis by age 13.
That said, Chambers pointed to a bigger-picture issue: Very few drugs have actually been studied in pregnant women, and fairly little is known about the safety of using any medication prenatally. The findings, published in the journal Pediatrics, are based on an examination of data from the Norwegian Patient Registry, which collected information from 112,973 babies born between 1999 and 2009, including 2246 with ADHD.
The increased risk of ADHD linked to longer use of acetaminophen might also be due to the severity of medical problems women had, not their use of the drug, said Dr. Chittaranjan Andrade of the National Institute of Mental Health and Neurosciences in Bangalore, India. The evidence is "much stronger" for a familial influence, since the disorder tends to run in families, he noted. Mothers filled out two questionnaires, one during and one after birth; fathers completed surveys on medication use 6 months before pregnancy.