Tylenol may reduce testosterone in male babies

New research suggests that women who take Tylenol during pregnancy—especially women who are pregnant with boys—might want to be careful about how long they take it.

In a study released this week, researchers at the University of Edinburgh grafted human testicular tissue onto mice and gave them daily doses of acetaminophen (the generic name for Tylenol, also called paracetamol) for either 24 hours or seven days. They found that there was no effect on testosterone production after 24 hours but that testosterone production was 45 percent lower after seven days.

Shinya Ito, head of clinical pharmacology and toxicology at The Hospital for Sick Children in Toronto, says this is a follow-up study to research that suggests a link between acetaminophen use during pregnancy and undescended testicles in male infants.

"There may be a clear biological link," says Ito, but he adds that the increased likelihood of undescended testicles in babies whose mothers had taken acetaminophen during pregnancy is small. The study's authors note that reduced testosterone production in the womb has also been linked to increased risks of infertility and testicular cancer later in life.

“We recommend that pregnant women follow current guidance and take the painkiller at the lowest effective dose for the shortest possible time,” says Rod Mitchell, one of the doctors behind the study.

The good news, says Ito, is that most people only take acetaminophen for a few days at a time. He recommends that pregnant women speak to their doctors about prolonged use of pain medication during pregnancy.

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