International guidelines for paracetamol use in pregnancy could be up for review following a study that shows it might contribute to reproductive disorders in male babies.

Just a week of regular paracetamol use in pregnancy could significantly reduce testosterone production in the fetus’ developing testes, according to research by the University of Edinburgh.

This matters because most common reproductive disorders in men can be linked back to a reduction in testosterone exposure in the growing fetus.

The study shows no effect on testosterone production following 24 hours of paracetamol treatment, but after seven days of paracetamol exposure the amount of plasma testosterone is reduced by 45%.

The British Medical Journal reports 4 previous studies have linked the use of paracetamol in pregnancy with an increased risk of an undescended testicle at birth in male babies (cryptorchidism).

This study indicates there is probably a critical time during pregnancy when the testes are developing and when paracetamol should be especially avoided, says co-author Dr Richard Sharpe, a male reproductive specialist.

This is likely to be in early pregnancy.

Commenting on the study, Dr Martin Ward Platt of the Royal College of Paediatrics and Child Health says the findings send a clear message that paracetamol comes with side-effects but cautions that fever during pregnancy can also be harmful to the developing embryo.

Therefore, small doses of the medication may be necessary.

25 May 2015 Amanda Davey

Last Reviewed: 26/05/2015

Reproduced with kind permission from


S. van den Driesche, J. Macdonald, R. A. Anderson, Z. C. Johnston, T. Chetty, L. B. Smith, C. McKinnell, A. Dean, N. Z. Homer, A. Jorgensen, M. E. Camacho-Moll, R. M. Sharpe, R. T. Mitchell, Prolonged exposure to acetaminophen reduces testosterone production by the human fetal testis in a xenograft model. Sci. Transl. Med. 7, 288ra80 (2015). (accessed May 2015).