Taking Tylenol or Excedrin while pregnant may increase the risk of attention deficit hyperactivity disorder-like problems in children, according to a recent study the Huffington Post reported.

Researchers from the University of California, Los Angeles found that pregnant women who frequently took acetaminophen, the active ingredient in most commonly used over-the-counter pain and fever reliever, were 40 percent more likely to have children later diagnosed with ADHD and similar issues, the Huffington Post reported.

More than 50 percent of women in the United States take acetaminophen when they are pregnant, researchers said.

"We aren't saying if you take one Tylenol once it will give your child hyperactivity," Dr. Beate Ritz, an epidemiologist at the University of California Los Angeles who worked on the study told NBC News. "You should just avoid chronic or long-term use."

For the study, researchers analyzed data o more than 64,000 Danish mothers and their children. They gathered information on pregnancy subject's acetaminophen use before problems in their children's learning or behavior would have become evident, The Los Angeles Times reported. Investigators tracked the study's pediatric subjects from their first trimester in utero for up to 15 years. 

They found that when the child's mother took acetaminophen during the last two trimesters of pregnancy, the probability of a child developing ADHD symptoms severe enough to require medication increased by 63 percent.  It also rose by 28 percent when acetaminophen was used in the third trimester alone, The Los Angeles Times reported. The risk was smallest - nearly 9 percent - when a pregnant woman reported taking the drug only during her first trimester of pregnancy.

"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."

The findings were recently published in JAMA Pediatrics.