New research suggests that males may have a higher risk of infertility if their mothers took Tylenol for extended periods during pregnancy. A study conducted by researchers at the University of Edinburgh and published in the journal Science Translational Medicine found that acetaminophen, the main active ingredient in Tylenol and Paracetamol, may inhibit production of testosterone. Researchers said that men have a higher risk of infertility, undescended testicles and testicular cancer when exposed to lower levels of prenatal testosterone.
Tylenol is currently recommended as safe for pregnant women suffering from fever and pain. The researchers used mice carrying grafts of human testicular tissue to test the effects of acetaminophen on testicular production. The mice received either a standard daily dose over 24 hours or seven days. Testosterone production was measured an hour after the final dose. The study found no effect in mice who had 24 hours of exposure. In the mice who were exposed for seven days, however, researchers saw that testosterone levels decreased by 45 percent.
Dr. Rod Mitchell of the University of Edinburgh said “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,”