The findings, published in JAMA Pediatrics on Monday, are preliminary and do not establish cause and effect. However, they do intensify questions about the risks and benefits of taking the medication while pregnant.
Aspirin and ibuprofen -- nonsteroidal anti-inflammatory drugs, or NSAIDs -- are generally not recommended as pain relievers for pregnant women, particularly during the last three months. Acetaminophen-based medications such as Tylenol, however, have generally been thought to be safe, and estimates suggest that more than 50 percent of women in the United States take acetaminophen at some point while pregnant.
"It is important we follow up [on] the potential health risks that acetaminophen may cause," Zeyan Liew, a Ph.D. candidate with the UCLA Fielding School of Public Health and an author on the study, told The Huffington Post. "ADHD incidence has been noticed to be increased in the last decades, and we are interested in searching for avoidable environmental factors that may contribute to the trend."
Liew and his co-authors looked at data on more than 64,000 women and their children taken from the Danish National Birth Cohort. They found that children whose mothers took acetaminophen while pregnant had a 13 percent to 37 percent greater risk of later being diagnosed with hyperkinetic disorder (which is similar to ADHD, but uses different diagnostic criteria), taking medications for ADHD, or displaying ADHD-like behaviors at age 7.
That link was stronger among women who took acetaminophen in multiple trimesters or who used it more frequently. For example, the risk of behavioral issues was elevated by 50 percent or more in children whose mothers took the pain reliever for more than 20 weeks while pregnant.
Image: Pregnant woman, via Shutterstock