Paracetamol, a common pain reliever considered safe for pregnant women, has for the first time been linked to an increased risk of attention deficit and hyperactivity disorder (ADHD) in children.

Researchers are pointing to paracetamol use as a new potential cause for the worldwide rise in cases of ADHD, a neuro-behavioural condition which has no known cause and affects as many as 5 per cent of children in the United States.

A study published in the Journal of the American Medical Association (JAMA) Pediatrics found women who took paracetamol - also known as acetaminophen - while pregnant, had a 37 per cent higher risk of having a child who would later be diagnosed with hyperkinetic disorder, a severe form of the condition.

Compared to women who did not take paracetamol while pregnant, women who did also had a 29 per cent higher chance of having children who were later prescribed medications for ADHD, and a 13 per cent higher chance of exhibiting ADHD-like behaviours by age seven.

Study should 'not change practice', lead author says

Previous research has suggested that paracetamol can interfere with normal hormone function and may affect the developing foetal brain.

The painkiller has also been linked to a slightly increased risk in boys of cryptorchidism, a condition in which the testicles do not descend.

The latest research was based on survey data on more than 64,000 Danish women from 1996 to 2002.

More than half said they took paracetamol at least once during pregnancy.

Outside experts cautioned that the observational findings do not prove that taking paracetamol-like pain relievers causes ADHD, only that a preliminary link between the two has appeared and would need to be confirmed by further research.

"Findings from this study should be interpreted cautiously and should not change practice," an accompanying editorial in JAMA Pediatrics by Miriam Cooper and colleagues at the Cardiff University School of Medicine said.

"However, they underline the importance of not taking a drug's safety during pregnancy for granted."

The reasons the women took the painkillers could have also had a confounding effect on the outcome, they added.

The study was led by Zeyan Liew, of the University of California, and was co-authored by Jorn Olsen of the University of Aarhus in Denmark.

AFP