Acetaminophen is classified as a mild analgesic. Commonly used for the relief of headaches and other minor aches and pains, it is a major ingredient in numerous cold and flu remedies.
The findings may help explain the reported associations between paracetamol use in pregnancy and reproductive health issues in young boys. Reduced exposure to testosterone in the womb has been linked to a raised risk of testicular cancer, infertility, and undescended testicles.
The research team note that more research is needed in order to establish the mechanism of how acetaminophen might have this effect.
Dr Rod Mitchell, a Wellcome Trust Intermediate Clinical Research Fellow at the university, said:
“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.”
Forty Five Percent Lower
In the study, researchers tested the effect of paracetamol on testosterone production, using mice that carried grafts of human testicular tissue. Such grafts have been shown to parrot how the developing testes grow and function during pregnancy.
Over a period of either 24 hours or seven days, the mice were given a normal daily dose of acetaminophen. The amount of testosterone produced by the human tissue was measured an hour after the final dose of paracetamol.
They found there was no effect on testosterone production following 24 hours of paracetamol treatment. After seven days of exposure, however, the amount of testosterone was reduced by 45 per cent.
The authors write in the abstract:
Protracted use of acetaminophen during pregnancy is associated with increased risk of cryptorchidism in sons, but effects on fetal testosterone production have not been demonstrated.
And they conclude:
Our results suggest that protracted use of acetaminophen (1 week) may suppress fetal testosterone production, which could have adverse consequences. Further studies are required to establish the dose-response and treatment-duration relationships to delineate the maximum dose and treatment period without this adverse effect.
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)