UCLA researchers say using acetaminophen, widely known as Tylenol, during pregnancy is linked to ADHD in children.
"Fifty-four percent of all women took it," said Dr. Beate Ritz.
Dr. Ritz and her colleagues examined the data of more than 64,000 women and their children in the National Danish Birth Cohort study.
They followed the babies until 11 years of age. They found moms who took the recommended doses of acetaminophen during pregnancy had nearly a 40-percent higher risk of having a child with attention-deficit-hyperactivity disorder compared to women who didn't take any. And the longer a pregnant woman took the pain reliever, the higher the risk.
"The duration of use throughout pregnancy was what was driving an increase," said Ritz.
In the study, researchers determined that acetaminophen may act as an endocrine disruptor, meaning it affects estrogen's activity in the body. And that may affect the development of a fetus's brain.
"The period of development that we are most concerned about is usually the fetal developmental, the nine months of pregnancy where a lot of the mechanisms are set in place," said Ritz.
So should pregnant women avoid acetaminophen? Dr. Ritz says women should talk to their doctors.
Dr. Ritz and her colleagues at the UCLA Fielding School of Public Health say they do believe environmental factors can lead to ADHD, and acetaminophen use may be just one of them.