Acetaminophen Use During Pregnancy Linked to Childhood Behavioral Problems, Study Finds

— -- A common over-the-counter pain medication has been associated with increased risk of developing behavioral issues for children who were exposed to the drug in utero, according to a study published today in the medical journal JAMA Pediatrics.

Children were more likely to exhibit behavioral issues, such as hyper-activity, if their mothers took acetaminophen while pregnant, according to the study by researchers from multiple institutions, including the University of Bristol in the United Kingdom.

Acetaminophen is a common pain reliever and fever reducer found in brands such as Tylenol. Expectant mothers have been told for years that reaching for the drug to treat pain during pregnancy is safe.

Dr. Evie Stergiakouli, lead author of the study and a researcher in genetic epidemiology and statistical genetics at the University of Bristol, said this study aimed to control for other variables -- such as genetic, familial or social factors -- so that researchers could get a better understanding of whether there's a link between the drug and behavioral conditions.

"We have evidence that acetaminophen use during pregnancy has a biological mechanism of action in regard to increasing behavioral issues during childhood," she told ABC News today.

However, the effect overall was relatively small and Stergiakouli emphasized that pregnant women should not panic if they are taking acetaminophen for pain relief and that avoiding taking the medication can be more dangerous, especially if a woman has a fever.

The researchers studied acetaminophen use in nearly 7,800 women living in Bristol, England, and then surveyed these women seven years later about their child’s behavior. They found that compared to women who did not take the drug during pregnancy, acetaminophen use during pregnancy was associated with a variety of behavioral issues in children.

Compared to the children of women who did not take the drug, children of women who did take acetaminophen had a 42 percent increased risk of conduct problems, a 31 percent increased risk in hyperactivity disorders and a 29 percent increased risk in emotional problems in their children, the study found.

Despite the increased risk for women taking the drug, the total risk of developing behavioral issues overall remained small, with 5 percent of children studied being affected by these behavioral issues.

“This does not mean it is not safe during pregnancy," Stergiakouli said.

"Women should still continue to use acetaminophen as required according to their physician, because the risk of not treating fever or pain can be much higher than risk of behavioral issues in offspring," she explained. For example, "fever increases the risk of pre-term labor if untreated during pregnancy."

She also stressed that further study is needed to understand the link between the drug and behavioral problems, and to identify any potential biological mechanism.

Rebecca Hoover, a pharmacist and clinical assistant professor of pharmacy practice and administrative sciences at Idaho State University, has studied this issue and said the new findings will help inform patients anxious about taking pain relievers and give them more information about the possible risks.

"It highlights the fact that we need to be careful about how much medications to use and when to use them and making sure we should be prudent," Hoover said.

Dr. Max Wiznitzer, a pediatric neurologist at Rainbow Babies & Children's Hospital, said the study provides valuable insight but that it was far too early to conclude the drug itself is a cause for the behavioral issues. Mothers in the study may not have reported all infections to researchers, he noted, or there could have been other issues that could account for why there's an association between taking the drug and behavioral issues.

"It's interesting but raises more questions that need to be addressed before you come to firm conclusions," he said.

American College of Obstetrics and Gynecology said there was not enough evidence to advise pregnant women to stop taking the medication.

“The study also has several limitations as it is not clear what dose of acetaminophen the mothers took, how long they took it, and for what reason,” ACOG officials said, though they noted that researchers did control for common conditions, such as headache and muscle pain, that often would lead women to take medication.

“The take-aways here are that physicians should not change clinical practice until definitive prospective research is done and, most importantly, patients should not be frightened away from the many benefits of acetaminophen," ACOG officials said.

The Consumer Healthcare Products Association, a national trade association representing the leading manufacturers and marketers of over-the-counter medicines and dietary supplements, said that more study was needed into this area of research.

“With regard to the study published in JAMA Pediatrics examining associations between reported use of acetaminophen by pregnant women and behavioral problems in their children, it is important for consumers to note that the study has many limitations,” CHPA officials said. “As with any study of associations (as opposed to cause and effect), there is always the possibility that there are other explanations for the observed results. There is no proven mechanism whereby acetaminophen might cause these effects, and it’s important to weigh the benefits and risks of treating pain and fever during pregnancy.”

Dr. Anish Ghodadra is a chief resident at the UPMC Department of Radiology in Pittsburgh and is currently working in the ABC News Medical Unit.