Children of women who use the painkiller acetaminophen during pregnancy may be at higher risk for attention-deficit/hyperactivity disorder (ADHD), according to a new Danish study.
Acetaminophen, also called paracetamol or the brand name Tylenol, is the most commonly used drug during pregnancy. For pregnant women suffering from common aches or fevers, doctors often recommend acetaminophen as a safer alternative to nonsteroidal anti-inflammatory drugs (NSAIDS) such as ibuprofen.
The new study included about 65,000 women in Denmark who gave birth between 1996 and 2002. Using the country's national medical database, researchers followed the children to see how many were diagnosed with ADHD, including a severe form of ADHD called hyperkinetic disorder.
More than half of the mothers in the study reported having taken acetaminophen during pregnancy, and the children of the mothers who took it were 13 to 37 percent more likely to be diagnosed with ADHD or hyperkinetic disorders by the time they were 7 years old.
The researchers also found a dose-response relationship between women's taking acetaminophen and their children's ADHD risk, meaning that the more often a woman took the drug during pregnancy, the higher the child's ADHD risk was. Children of women who reported using acetaminophen for 20 or more weeks during pregnancy had almost double the risk of hyperkinetic disorders, the researchers said. [7 Ways Pregnant Women Affect Babies]
The results held when the researchers accounted for mothers' inflammation or infection during pregnancy, their mental-health problems or other factors that could affect ADHD risk, according to the study, published Feb. 24 in the journal JAMA Pediatrics.
The findings might explain some of the increase in rates of ADHD in the past decades, but more research is needed to show whether there is a cause-and-effect relationship between the drug and ADHD, the researchers said.
Acetaminophen is generally considered a safe drug for pregnant women to take, but recent findings have suggested that it may have some hormone-disrupting properties that could affect the normal brain development of the fetus, the researchers said.
A review study in 2011 pointed to a link between a woman's acetaminophen use during pregnancy and children's risk for asthma. In another study, published in October, researchers found that children whose mothers used acetaminophen for more than 28 days during pregnancy had poorer motor development and communication, as well as higher activity levels when they were 3 years old, compared with their siblings.
However, none of these studies have proven that acetaminophen use during pregnancy causes health risks for children. More work is required to understand whether other factors underlie the link, experts say.
"This study alone should not change practice. Nonetheless, it highlights some important messages," wrote Miriam Cooper, a psychologist at Cardiff University School of Medicine, in an editorial accompanying the study. The findings "underlie the importance of not taking a drug’s safety during pregnancy for granted," Cooper said.
Although the researchers controlled for many confounding factors, there still remains a possibility that some factors were not accounted for, Cooper said.
"Although it is a strength that fever, infections and inflammatory conditions were accounted for in the study, these might not be the only reasons why pregnant women might take acetaminophen," Cooper said.
Cooper also noted that taking acetaminophen may be a question of weighing risks and benefits. Fever during pregnancy is linked to health problems in children, studies have shown. Taking acetaminophen to reduce the fever may lessen some of those risks.
One study in 2012 found that having a fever or flu during pregnancy is linked with autism in children, and another study in the same year found that pregnant women who don't treat their fever may be increasing the child's risk for autism.
Live Science newsletter
Stay up to date on the latest science news by signing up for our Essentials newsletter.