Researchers have found a link between women taking acetaminophen—the active ingredient in Tylenol—during pregnancy and cases of attention-deficit hyperactivity disorder in their kids.
Published Monday in the journal JAMA Pediatrics, the results show that the ingredient "may influence brain development in utero," the Los Angeles Times writes.
The study looked at more than 64,000 Danish women and found that children whose mothers took the medication during their pregnancy were 29 percent more likely to be diagnosed with ADHD than those whose moms did not take the drug.
That risk was even greater—a 63 percent increase—if the mothers took the medication during their second and third trimesters.
"We used to count a baby's 10 fingers and 10 toes and assume that any drug his mother took must have been safe," Dr. Daniel Kahn, a UCLA obstetrician not involved in the research, tells the Times.
"The lowest exposure is always the best, for any agent," he adds, referring to medication taken during pregnancy.
However, the Times reports, "the findings do not establish that prenatal exposure to acetaminophen ... caused the observed increase in hyperactivity disorders."
In fact, an editorial accompanying the study warned doctors and pregnant women that they should not change their health-care routines based on a single study.