Pregnant women should avoid taking painkillers containing paracetamol because doing so may affect the development of their child. (Photo: Shutterstock)

Painkiller use during pregnancy damages baby boys' testicle development

Over the counter painkillers have a negative effect on boy embryos' production of testosterone, shows new study.

Paracetamol, the main component in over the counter painkillers, can damage the testicles of embryos and reduce the amount of testosterone they produce, shows a new study.

The scientists behind the study believe this may explain evidence that pregnant women's use of painkillers is linked to an increased risk of deformed testicles and cryptorchidism, where the testicles do not fall properly into place.

"This is the first time that a study of human testicles from embryos shows that the compound paracetamol almost halved the production of testosterone after seven days of use," says Rob Mitchell, a researcher at the University of Edinburgh in an email to He is the lead researcher behind the new study which has just been published in the journal Science Translational Medicine.

Mice given testicle tissue from human embryos

In the study, the team of researchers from the University of Edinburgh and Copenhagen University inserted testicle tissue from human embryos into castrated male mice. They then divided the mice into groups and gave them varying doses of paracetamol.

The researchers discovered that when the mice were given the equivalent of a human dose of paracetamol three times a day for seven days, their testicle tissue secreted 45 per cent less testosterone than those in the group that were given no paracetamol.

A single daily dose of the painkilling substance has no effect on the release of testosterone.

"This is an exciting and convincing study. Paracetamol seems to have a rather extreme effect on testosterone production. It is, however, not certain that it would affect humans to the same degree. A pregnant woman taking one tablet of paracetamol three times a day for seven days in a row won't necessarily have the same effect on her embryo as what we find here," says Professor Cecilia Ramlau-Hansen from the Department of Public Health at Aarhus University.

She was not involved in the new study but studies the effects of various substances on human fertility.

Scientists have previously shown that the more types of over the counter painkillers pregnant women take, the greater risk they face that their baby boys will be born with testicle deformities.

Human studies are difficult to conduct

It is difficult to conduct controlled human studies in this field as it would require that scientists gave pregnant women paracetamol in small and large doses so as to be able to compare and study the effects on the embryo.

But such experiments might harm the child. This is why the new study is one of the closest to a human trial conducted to date, says Ramlau-Hansen.

"It’s not permitted to conduct experiments on humans involving the prescription of substances with the potential of causing serious permanent damages on the mother or the child. The scientists therefore attempted to get as close to a human model as possible by inserting human tissue in a mouse," says Ramlau-Hansen.

Danish women take a lot of painkillers

A study shows that about 50 per cent of Danish women have taken painkillers during pregnancy. The question is how many of them took pills for a few days and how many took them over an extended period during pregnancy, says Ramlau-Hansen.

"The study suggests that the longer women take painkillers, the greater the risk there is of their embryos sustaining damage. So if they want to be on the safe side, women should avoid taking painkillers during pregnancy unless absolutely necessary," says Ramlau-Hansen

She emphasises that most women are aware of what they should try to avoid painkillers while pregnant.


Read the Danish version of this article on

Translated by: Hugh Matthews

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