A common pain reliever considered safe for pregnant women has been linked for the first time to an increased risk of attention deficit and hyperactivity disorder (ADHD) in children.
More studies of paracetamol are needed to confirm the findings, but experts said new research points to a new potential cause for the worldwide rise in cases of ADHD, a neuro-behavioural condition that has no known cause and affects as many as 5 per cent of US children.
Women who took paracetamol, also known as acetaminophen, while pregnant had a 37 per cent higher risk of having a child who would be later given a hospital diagnosis of hyperkinetic disorder, a particularly severe form of ADHD, said the study published in the February 24 edition of the Journal of the American Medical Association (JAMA) Pediatrics.
Against women who didn't take paracetamol while pregnant, women who did also had a 29 per cent higher chance of having children who were later prescribed medications for attention deficit hyperactivity disorder, and a 13 per cent higher chance of exhibiting ADHD-like behaviours by age seven.
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 research was based on survey data from more than 64,000 Danish women between 1996 and 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 Tylenol-like pain relievers causes ADHD, only that a preliminary link between the two had appeared and would need to be confirmed by further research.
''Findings from this study should be interpreted cautiously and should not change practice,'' said an accompanying editorial in JAMA Pediatrics by Miriam Cooper and colleagues at the Cardiff University school of medicine. ''However, they underline the importance of not taking a drug's safety during pregnancy for granted.''
The study was led by Zeyan Liew, of the University of California, Los Angeles, and was co-authored by Jorn Olsen of the University of Aarhus in Denmark.