Aspirin and other anti-inflammatory drugs given to newborn rats change their sexual behaviour later in life. The drugs interfere with the brain’s sex-specific development, suggesting that they may also affect equivalent mechanisms in humans.

In theory, mothers taking so-called non-steroidal anti-inflammatory drugs (NSAIDs) might pass on high levels to their baby via the placenta. The list of NSAIDs includes paracetamol (tylenol), aspirin and indomethacin (indocin), which prevents premature labour.

But the researchers caution that, until similar effects have been found in people, expectant mothers should not change their use of medication.

“I don’t want to panic pregnant women,” says Margaret McCarthy, who carried out the study at the University of Maryland, Baltimore, US, with her colleague Stuart Amateau. She says women are already advised to avoid taking unnecessary drugs.

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