Acetaminophen, sold over-the-counter as Tylenol and other brand names, is generally regarded as a safe and effective pain reliever when used as directed. But a growing body of evidence is calling into question its use during pregnancy. Studies have linked the use of the drug by expectant mothers to poorer early language development and sleep and behavioral issues in children.
Now, a new study by researchers at the University of Illinois at Urbana-Champaign has added more evidence to the link between maternal acetaminophen usage and early childhood attention and behavioral problems. Their research was published in the January-February 2004 issue of the journal Neurotoxicology and Teratology.
The new research was conducted as part of the Illinois Kids Development Study that follows women from early pregnancy and their children from birth through middle childhood to investigate the impact of prenatal exposures to chemicals and other environmental factors on development.
For the acetaminophen study, researchers enrolled 535 participants between December 2013 and March 2020. Mothers were interviewed about their use of medications six times during pregnancy—at approximately 10–14, 16–18, 22–24, 28–30, and 34–36 weeks of gestation, and within 24 hours of the child’s birth. When the children were 2, 3, and 4 years of age, caregivers completed the Child Behavior Checklist for ages 1.5–5 years (CBCL), which consists of 100 questions divided into internalizing behaviors and externalizing behaviors and further divided into other subscales. More than 300 children were assessed at age 2, with 262 assessed again at 3, and 196 at age 4.
After accounting for other factors that may affected the outcome, the researchers found modest but noticeable increases in problems with attention and behavior in children whose mothers used more acetaminophen during pregnancy.
“Our most important finding was that with increasing acetaminophen use by pregnant participants, especially during the second trimester, their children showed more attention-related problems and ADHD-type behaviors, which we call ‘externalizing behaviors,’ at every age we measured,” said lead researcher Megan Woodbury, PhD, now a postdoctoral researcher at Northeastern University in Boston.
The researchers are quick to point out that their findings are not an indication that the children have attention-deficit/hyperactivity disorder or that they will be diagnosed with ADHD in the future. But the children seem to be having more trouble with attention than peers of the same age who were less exposed or not exposed at all to acetaminophen in the womb.
Woodbury, who is pregnant herself, says she doesn’t want to scare other expectant mothers away from using acetaminophen when needed. Extreme headaches or other painful episodes and fevers can be debilitating and even dangerous, requiring the use of effective pain medication. She said she has turned to acetaminophen once per trimester so far, but she avoids it for minor aches, pains, or slight fevers.
More research is needed to test whether frequent use of acetaminophen during the second trimester of pregnancy may be particularly problematic for the developing brain, the researchers said. “This study suggests that the second trimester of fetal development may be a sensitive window of exposure for acetaminophen exposure,” they wrote in their conclusion. “These results can inform future research design to investigate potential mechanisms and examine whether similar results are observed in larger and more diverse cohorts in order to establish whether there is strong causal evidence.”