Pregnant women should avoid longer-term use of paracetamol, a UK study concluded after tests on mice showed it the pain killer stopped the body from producing testosterone.

The lack of testosterone can lead to birth deformities like undescended testicles in boys, the BBC reported, quoting Danish research.

Using the over-the-counter drug has always come with guidelines, but the study found prolonged use over seven days may lead to reproductive problems in the womb.

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Lead researcher Dr Rod Mitchell told the BBC: “This study adds to existing evidence that prolonged use of paracetamol in pregnancy may increase the risk of reproductive disorders in male babies.

“We would advise that pregnant women should follow current guidance that the painkiller be taken at the lowest effective dose for the shortest possible time.”

Paracetamol is one of the few painkillers pregnant women can take. It is recommended for fevers which can also be harmful to unborn children.

The study was published in the journal Science Translational Medicine.