Pregnant women who take acetaminophen -- best known under the brand name Tylenol -- might be more likely to have a child with attention deficit-hyperactivity disorder (ADHD), a new long-term study suggests, Newsmax Health reports.

Children whose mothers took acetaminophen while pregnant had up to a 40 percent higher risk of being diagnosed with ADHD, according to the research, which involved more than 64,000 Danish mothers and their children. The kids were born between 1996 and 2002.

What's more, the ADHD risk appeared to increase with the amount of acetaminophen the mother reported taking during pregnancy, explained study co-author Dr. Beate Ritz, head of the epidemiology department at the University of California, Los Angeles (UCLA).

"The strongest effects were seen when a woman said she had taken it for six weeks or more, and even more strongly at 20 weeks or more," Ritz added. "We always thought acetaminophen is kind of harmless and not so bad to take during pregnancy, and probably it is, if you take it once or twice. But if you take it repeatedly, you see these risks creeping up."

The maker of Tylenol, McNeil Consumer Healthcare, said in a statement that the medication's label directs women who are pregnant or breast-feeding to consult with a health care professional before using the product.

In their analysis, the researchers took into account the possibility that children's ADHD had been caused by maternal diseases that prompted the use of acetaminophen.