Women who take common pain killer acetaminophen (paracetamol) in pregnancy are at a greater risk of having a child with attention deficit hyperactivity disorder (ADHD), research reveals.
This is according to a pilot study recently published in Journal of the American Medical Association (JAMA) Pediatrics.
For the study, researchers from UCLA in the US and University of Aarhus in Denmark selected 64,322 children and their mothers. All the participants were part of the Danish National Birth Cohort, between 1996 and 2002.
Acetaminophen use during pregnancy was determined using computer-assisted telephone interviews that were conducted up to three times during pregnancy and again six months after childbirth.
They first asked parents about any behavioural problems in their children using the Strength and Difficulties Questionnaire, a standard behavioural screening questionnaire used by scientists.
It also assessed five domains, including emotional symptoms, conduct problems, hyperactivity, peer relationship and social behaviour in children and adolescents between the ages of 4 and 16.
The researchers found that children whose mothers used acetaminophen during pregnancy were at a 13% to 37% higher risk of later receiving a hospital diagnosis of hyperkinetic disorder, being treated with ADHD medications or having ADHD-like behaviours at age 7.
The longer acetaminophen was taken — that is, into the second and third trimesters — the stronger the associations.
The risks for hyperkinetic disorder/ADHD in children were elevated 50% or more when the mothers had used the common painkiller for more than 20 weeks in pregnancy.
Researchers say the data raises the question of whether the paracetamol should be considered safe for use by pregnant women.
"The causes of ADHD and hyperkinetic disorder are not well understood, but both environmental and genetic factors clearly contribute," said Dr Beate Ritz, professor and chair of the department of epidemiology at the Fielding School and one of the senior authors of the paper.
"We know there has been a rapid increase in childhood neurodevelopmental disorders, including ADHD, over the past decades, and it's likely that the rise is not solely attributable to better diagnoses or parental awareness. It's likely there are environmental components as well."
"That gave us the motivation to search for environmental causes that are avoidable," said the University of Aarhus' Dr. Jørn Olsen, another senior author and former chair of the UCLA Fielding School's epidemiology department.
"Part of the neuropathology may already be present at birth, making exposures during pregnancy and/or infancy of particular interest. Because acetaminophen is the most commonly used medication for pain and fever during pregnancy, it was something we thought we should look at."
"It's known from animal data that acetaminophen is a hormone disruptor, and abnormal hormonal exposures in pregnancy may influence fetal brain development," Ritz said.
"We need further research to verify these findings, but if these results reflect causal associations, then acetaminophen should no longer be considered a 'safe' drug for use in pregnancy," Olsen said.
Local experts urged caution and said the study shouldn’t cause women to stop using paracetamol.
Clinical senior lecturer at Deakin University Michael Vagg told The Conversation that the JAMA Pediatrics study “may be a random finding which will go away when attempts to replicate it are made.”
“We don’t have a firm idea exactly how paracetamol works, so the idea it could influence developing foetal brains in some way is not inherently implausible.
“There is, however, a huge amount of experience with paracetamol in pregnancy which has not previously suggested a link.”
Dr Vagg said expectant mothers should try to manage day-to-day pains with hot or cold packs, rest and pacing of activities before using medications. But those with chronic pain problems who become pregnant should discuss their options with their GP or pain specialist, he said.
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