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WOMEN who take paracetamol while pregnant are more likely to have “less manly sons”, a study suggests.

Male mice exposed to the painkiller in the womb were less aggressive and had a lower sex drive as adults. Researchers say the drug is linked to “reduced masculinisation of the adult brain”. Doses used in the study are comparable to those regarded as safe for pregnant women.

The scientists from the University of Copenhagen have called for the advice to be revised as a result. Affected male mice were less likely to mark their territory with urine or fight off rivals. They were just as likely to sniff females in a sexual way and more likely to “mount” them – but were less likely to penetrate or ejaculate.

Previous studies by the same scientists have shown prenatal exposure to paracetamol may cause developmental changes in the reproductive organs in mice and humans.

This includes female infertility among adult mice and deformities in new-born boys.Researchers say the findings are of particular concern because paracetamol is routinely recommended by doctors as safe for use while pregnant.The NHS Choices website says: “Paracetamol has been used routinely during all stages of pregnancy to reduce a high temperature and for pain relief.

“There is no clear evidence that it has any harmful effects on an unborn baby.

“However, as with any medicine taken during pregnancy, use paracetamol at the lowest effective dose for the shortest possible time.

“If the recommended dose of paracetamol doesn’t control your symptoms or you’re in pain, get more advice from your midwife or GP.”

Study leader Anders Hay-Schmidt said: “Male mice exposed in utero to paracetamol exhibited changes in urinary marking behaviour as adults and had a less aggressive territorial display towards intruders of the same gender.

“Additionally, exposed males had reduced intromissions and ejaculations during mating with females in oestrus.

“Together, these data suggest that prenatal exposure to paracetamol may impair male sexual behaviour in adulthood by disrupting the sexual neurobehavioral programming.

“These findings add to the growing body of evidence suggesting the need to limit the widespread exposure and use of paracetamol by pregnant women.”

Dr Rod Mitchell, from the University of Edinburgh, said: “It is important to recognise that management of pain and fever during pregnancy are important for the health of mother and baby.

“This new study therefore reinforces the current recommendation from the Department of Health that pregnant women should only use paracetamol for the minimum period necessary to provide symptomatic relief of pain and fever.”

Dr Ali Abbara, from Imperial College London, said: “A useful principle is to use as few medications that are not essential for health for as short a duration of time as is possible during pregnancy.”

Professor Ieuan Hughes, from the University of Cambridge, said: “In the animal study exposure to paracetamol was daily from seven days post-coitum to birth.

“Pregnant women generally take analgesics like paracetamol intermittently for symptoms and generally for a very short period.

“While the study provides interesting data and adds to the body of evidence that analgesics like paracetamol can affect the reproductive tract (and now brain) in rodents, it is my view that there is not sufficient evidence in humans to deter pregnant women taking the occasional paracetamol for symptomatic reasons.”

The findings are published in the journal Reproduction.