A recent study out of Copenhagen uncovered that use of the popular painkiller Tylenol by pregnant women could reduce masculinity in male offspring. Exposure to Tylenol in utero has also been linked to decreased fertility in females, and more controversially to ADHD and Autism among children. Although further research is necessary to confirm the results, pregnant women should be alerted of the possible impact Tylenol could pose to the developing child.
In a study published by the University of Copenhagen, researchers administered paracetamol, the pain relieving substance found in Tylenol, to pregnant rats. The scientists found that administering the drug to the pregnant mice led to reductions in masculinity among male offspring. Paracetamol decreased the production of testosterone, the male sex hormone, which aids in mediating typical male characteristics, such as aggression and territoriality. The resulting reductions in masculinity hindered the abilities of survival and reproduction among the rats. In fact, paracetamol disabled some male rats from mating with females.
Dr. David Møbjerg Kristensen, one of the researchers involved in the University of Copenhagen study, explained:
In a trial, mice exposed to paracetamol at the fetal stage were simply unable to copulate in the same way as our control animals [those unexposed to paracetamol]. Male programming had not been properly established during their fetal development and this could be seen long afterwards in their adult life. It is very worrying.
Paracetamol, also called acetaminophen, is responsible for the pain-relieving qualities of Tylenol. Under the recommended dosage, Tylenol is assumed safe and widely used by expectant mothers as a non-opioid analgesic, meaning it treats minor pains, headaches, and fevers. According to Tufts University, although it is unclear how exactly paracetamol works in the body, the medication is believed to inhibit a substance that regulates heat and pain in the brain. The substance works on the hypothalamus, the part of the brain associated with homeostatic functions, which maintains the balance of the body’s systems. The results from the University of Copenhagen would not mark the first instance of controversy for Tylenol.
In 2016, the University of Copenhagen published a study on the effects of female rats exposed to paracetamol in utero. The study concluded that female rats exposed to paracetamol were born with fewer eggs in their ovaries compared to the other mice, hinting decreased fertility levels due to the drug. According to the National Institute of Health, a study out of Spain found a link between paracetamol consumption by pregnant women and prevalence of Autism and Attention Deficit Hyperactivity Disorder among offspring. However, the study did not take into account other relevant variables, such as how pain or fever impacted the developing child in utero, so there is insufficient evidence that Paracetamol was the direct cause of such disorders.
Further research is needed to confirm the results of paracetamol on masculinity. The importance of the findings by the University of Copenhagen is staggering, as many women use Tylenol during pregnancy after being informed that it is safe for their babies. Dr. David Møbjerg Kristensen explains that a possible limitation to the study’s findings is that the testing subjects were rats, meaning the results could differ for humans. The researchers note that due to the possible grave consequences of paracetamol on masculinity and female fertility, conducting a study on people many never occur out of ethical concerns. For now, pregnant women might want to be careful to use painkillers containing paracetamol even if directed by a physician.