Tylenol During Pregnancy Could Harm Male Babies, Study Shows

Taking too much Tylenol during pregnancy could reduce testosterone levels in male babies, according to a new study.

The study, published in Science Translational Medicine, found that prolonged use of acetaminophen, the drug in Tylenol, by a pregnant mother reduced production of testosterone in her unborn son.

The study used mice that carried grafts of human tissue. After one day of exposure to the drug there was no effect on testosterone production, but after seven days the amount of testosterone was down by 45 percent.

Limited testosterone in the womb is related to increased risk of infertility, testicular cancer and undescended testicles.

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“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,” said Rod Mitchell, one of the authors of the study from the University of Edinburgh.

Acetaminophen drugs like Tylenol or Panadol are the most common medicine for managing pain or fevers during pregnancy.

Write to Tessa Berenson at tessa.berenson@time.com.