The study by UCLA and the University of Aarhus in Denmark found an increased likelihood of ADHD nearly doubled when mothers used the painkiller for more than 20 weeks during pregnancy, UCLA's website reported.
The study was published in JAMA Pediatrics. Children and mother's were enrolled from 1996 to 2002 and at each trimester mothers were asked if they had used acetaminophen, Fox News reported. The study followed up with the same women when their children were 7 years old and asked about behavioral patterns and prescription rates of medicines such as Ritalin.
Forbes reported that the study found that the chances a child would end up being prescribed an ADHD medication later on rose by 50 percent. The story noted that acetaminophen – the active ingredient in medications such as Excedrin and Tylenol – can cross the placenta and make its way to the fetus.
The authors of the study state that it is plausible that acetaminophen could interrupt fetal brain development by interfering with maternal hormones or through neurotoxicity.
However, Forbes notes that the study could not establish "causation," only a correlation between the use of acetaminophen and later behavior problems.