Taking paracetamol during pregnancy is linked to autism and ADHD in children, a new study claims.
Boys whose mothers took the painkiller while expecting were more likely to be on the autistic spectrum while it was associated with higher rates of ADHD in both sexes.
Official guidelines say paracetamol should be taken only if necessary in pregnancy and for the shortest possible time.
The latest study by Spanish researchers suggests children regularly exposed to the common medication while in the womb were more likely to show signs of both conditions.
In what has been hailed the first study of its kind, it looks at the association between the use of this drug in pregnancy and autism spectrum symptoms in children.
Scientists say it is also the first study to report different effects on boys and girls.
They found those whose mothers took the drug regularly were 30 per cent more likely to to show impaired attention functions and an increase of two clinical symptoms of autism spectrum symptoms in boys.
The study recruited 2,644 mother-child pairs in a birth cohort study during pregnancy.
Of these, 88 per cent were evaluated when the child was one year old, and 79.9 per cent were evaluated when they were five years old.
Mothers were asked about their use of paracetamol during pregnancy and the frequency of use was classified as never, sporadic, or persistent.
Exact doses taken could not be noted as the mothers were unable to recall them precisely.
It found 43 per cent of children evaluated at age one and 41 per cent assessed at age five were exposed to any paracetamol at some point during the first 32 weeks of pregnancy.
When they were again assessed at age five, exposed children were at higher risk of hyperactivity or impulsivity symptoms.
Persistently exposed children in particular showed poorer performance on a computerised test measuring inattention, impulsivity and visual speed processing, the study found.
Boys also showed more symptoms of autism when persistently exposed to paracetamol.
Dr Jordi Julvez, a researcher at the CREAL institute in Barcelona and the study’s co-author, said: “Paracetamol could be harmful to neuro-development for several reasons.
“First of all, it relieves pain by acting on cannabinoid receptors in the brain.
“Since these receptors normally help determine how neurons mature and connect with one another, paracetamol could alter these important processes.
“It can also affect the development of the immune system, or be directly toxic to some foetuses that may not have the same capacity as an adult to metabolise this drug, or by creating oxidative stress.”
The research also revealed that children who were persistently exposed performed worse on computerised tests measuring inattention, impulsively and visual speed processing.
Meanwhile, before any changes to treatment recommendations are made, scientists say that further studies should be conducted including more precise dosage measurements.