Avoid Tylenol because of autism risks? Not so fast, says this Kansas scientist.
U.S. Health and Human Services Secretary Robert F. Kennedy Jr., joined by President Donald Trump, delivers an announcement on “significant medical and scientific findings for America’s children” in the Roosevelt Room of the White House on Sept. 22, 2025 in Washington, D.C. (Photo by Andrew Harnik/Getty Images)
“Don’t take Tylenol!” I overheard one of my nursing students say as I returned after a break to the class. This was after a physician had shared that one of his patients told him to learn more the risks of Tylenol.
Confusion about Tylenol, which is considered a Pregnancy Category B substance safe for use throughout pregnancy, has surged after President Donald Trump and Health Secretary Robert F. Kennedy Jr. suggested at a news conference that there might be a correlation between the medication and autism spectrum disorders. To date, no consistent association has been found.
A study on the subject comes from some of the country’s premier researchers, including Andrea Baccarelli from Harvard’s Chan School of Public Health. In this paper, a new method called Navigation Guide Methodology uses meta-analyses and other statistical analyses to scrutinize existing evidence. Their results suggest that pregnant women limit Tylenol use. Their method uses data to fast-track development of recommendations that help prevent harmful exposures of humans to environmental agents in the environment.
Establishing a causal association has been difficult in this situation. First, conducting randomized controlled studies — in which participants are randomly given a drug or not and variables in the environment are controlled — on pregnant women is not feasible and ethically abhorrent. Second, laboratory research on this topic is still scant and unclear. One theoretical study suggested that the NAPQ1-breakdown product of acetaminophen (the active ingredient in Tylenol) can cause in utero mitochondrial damage.
However, many of these newer studies exhibit the same limitations as earlier research. That is, reliance on maternal self-report; lack of detailed data on dosage, duration and timing of exposure; as well as failure to control for genetic and familiar confounders.
While existing studies suggest an association between heavy use of Tylenol and autism spectrum disorders, a causal relationship remains to be established. Tylenol use in mice has been shown to cause defects in cartilage development by negatively affecting genes that control limb development. Cartilage malformations have also been noted in zebrafish embryos exposed to Tylenol. Some researchers point to the presence of hypermobility and abnormal gait in people with autism spectrum disorders and ADHD as a corollary to Tylenol exposure in the womb.
Another animal study treated pregnant mice with 100 or 400 mg/kg a day in the second trimester, or 400 mg/kg a day in the second or third trimester and examined maternal fetal blood phenotypes, pregnancy results and organ development. It found that some lipids, enzymes and hormones were changed. Researchers also observed that Tylenol administration stunted the formation of connections in the developing hippocampus.
There was an observational follow-up study on 2.5 million children in Sweden born between 1995 and 2019. This study used sibling control analysis — looking at and controlling for factors such as genes and the environment shared between families — and found that previously reported associations were absent.
This indicates that any associations were likely the results of familial confounding: when families share genes and the environment. For instance, a mother’s genetic risks for ADHD could also predispose her to headaches and infections that might require Tylenol use. People would likely link the ADHD in the child to Tylenol, use even though it was the mother’s ADHD that led to her use of the drug.
What happens if you do not treat high fever during pregnancy? In fact, high fever during pregnancy, even hot temperatures from saunas and bathtubs, can cause severe damage to the developing fetus, including neural tube defects, craniofacial deformities and congenital heart defects.
Public health experts and medical bodies are resisting. The American Academy of Pediatrics denounced the announcement linking Tylenol with autism. FDA Commissioner Martin Makary downplayed the warnings from Human and Health Services in a letter to American physicians that encouraged minimization of use during low-grade fevers and stressed the lack of any causal relationship as well as the fact that Tylenol remained the safest painkiller during pregnancy.
However, a concerning development is the decision by the FDA to change labels on products that contain acetaminophen, which remains the only over-the-counter drug to treat fever during pregnancy.
Association does not mean causation. More research data will be needed before recommending that pregnant women avoid Tylenol to prevent neurodevelopmental disorders in the newborns.
Syed Jamal teachers college-level chemistry, biology and anatomy/physiology and researches phytoremediation and cancer biology. Through its opinion section, Kansas Reflector works to amplify the voices of people who are affected by public policies or excluded from public debate. Find information, including how to submit your own commentary, here.