Reproductive Headache? Investigating Acetaminophen as a Potential Endocrine Disruptor

The presumed safety profile of acetaminophen hasmade it a popular choice of painkiller among pregnant women.12 In fact, acetaminophen, also known as paracetamol, is the only analgesic that the U.S. Food and Drug Administration (FDA) considers safe, when used as recommended, to take throughout pregnancy. However, researchers have found evidence that acetaminophen—although still considered the safest pain reliever for pregnant women—may interfere with the action of some key hormones in utero. “There’s a perceived notion that because a medicine is overthe-counter [OTC], its use has been well studied in pregnancy,” says Christina Chambers, a reproductive and perinatal epidemiologist at the University of California, San Diego. But that is not necessarily the case. In reality, she explains, only limited pregnancy safety data are available for most OTC products, and safety recommendations are often based on assumptions rather than on rigorous evidence. The FDA gives acetaminophen a “B” rating for pregnancy risk in all three trimesters, meaning that animal studies have shown no risk of congenital birth defects but that effects in pregnant women have been either not studied or not confirmed. This lack of research means that acetaminophen is being used with what some experts say is an unclear prenatal safety profile. At the same time, “Acetaminophen certainly is no thalidomide,” says Danish biologist David Kristensen, an assistant professor at the University of Copenhagen, referencing the notorious drug for morning sickness that caused severe birth defects in the 1950s and 1960s. The associations noted in studies to date— most commonly between acetaminophen exposure and abnormalities in the male reproductive tract—are quite subtle, Kristensen says. He adds, however, that one must consider how many women use the drug in pregnancy. “When millions of pregnant women are using acetaminophen worldwide, even a low [potential] risk becomes concerning,” he says. In one 2005 analysis of data from two large U.S. case–control studies, roughly two-thirds of the pregnant women surveyed reported taking acetaminophen at some point during their pregnancy. Nearly 60% of these women had taken it during the first trimester, a period of rapid fetal development. Other studies have also reported common use of acetaminophen during pregnancy.789