U.S. Secretary of Health and Human Services Robert F. Kennedy Jr. may be setting his sights on acetaminophen, the active ingredient in Tylenol, as a root trigger of autism spectrum disorder. HHS is purportedly planning to list acetaminophen use during pregnancy as a risk factor for autism in its much-awaited report later this month.
The Wall Street Journal first broke the news of HHS planning to link acetaminophen to autism over the weekend, citing “people familiar with the matter.” The report will reportedly also lay blame on low levels of folate (vitamin B9) as a potential cause of the developmental disorder. While some studies have suggested a possible connection between acetaminophen and autism, others haven’t, and many experts have argued there’s not enough evidence at this time to definitively promote such a link.
The case for and against acetaminophen in autism
Though similar medications like nonsteroidal anti-inflammatory drugs (NSAIDs) have their advantages, acetaminophen remains the most widely used over-the-counter painkiller and fever reducer in the world.
Like every drug, though, acetaminophen has its side effects. Chronic use or excessively high doses can potentially trigger acute liver or kidney damage, and acetaminophen is known to be the most common cause of acute liver failure from drug overdose in the U.S. Overall, however, acetaminophen is thought to be safer and more tolerable to take than aspirin or NSAIDs, making it an appealing pain and fever treatment for women during pregnancy.
That said, some studies over the years have pointed to possible complications from taking acetaminophen during pregnancy. Just last month, a review published by Mount Sinai researchers found that prenatal exposure to acetaminophen could increase the risk of several neurodevelopmental disorders, including autism and attention-deficit/hyperactivity disorder (ADHD). The researchers also noted that acetaminophen can cross the placental barrier, and they speculated that its presence may harm fetal brain development by causing oxidative stress or the disruption of certain key hormones.
It’s not at all clear yet that Tylenol can cause autism, however, and there’s reason to believe that many positive studies have failed to account for the noise in the data.
Last year, for instance, researchers in Sweden and the U.S. conducted a sweeping analysis of all children born in Sweden between 1995 and 2019. They initially found a slightly increased risk of autism in children whose mothers reported acetaminophen use during pregnancy in the raw data. However, when they only compared siblings to each other, they failed to find any increased autism risk linked to the drug.
Autism is likely caused by a mix of genetic and environmental influences. And since siblings share many of these influences, these sorts of studies are better able to analyze risk factors that differ between one pregnancy and the next (in this case, acetaminophen use). Since women who use acetaminophen could have an increased risk of health conditions or other factors that make their children more vulnerable to autism, acetaminophen may simply be a red herring, the researchers noted.
“Results of this study indicate that the association between acetaminophen use during pregnancy and neurodevelopmental disorders is a noncausal association,” the study authors wrote in their paper, published April 2024 in JAMA. “Birthing parents with higher acetaminophen use differed in many aspects from those with lower use or no use.”
No smoking gun
Though it’s possible some external factors may be helping increase the prevalence of autism, many experts believe that reported cases have largely increased due to better detection and expanded criteria for diagnosing autism. And given the shaky evidence supporting a link between acetaminophen and autism, plenty of researchers are already voicing their skepticism of the HHS report’s expected conclusions (in a statement to the WSJ, HHS declined to confirm the report’s contents until publication).
The Coalition of Autism Scientists is a group that formed in the wake of RFK Jr.’s announcement earlier this April to examine the causes of autism. The coalition currently includes more than 200 researchers in the field from across the country. It’s unsurprisingly not on board with Kennedy.
“It is highly irresponsible and potentially dangerous to claim links between potential exposures and autism when the science is far more nuanced and uncertain,” the coalition explained in a statement released Monday. “Secretary Kennedy’s announcement will cause confusion and fear. He seems to be cherry-picking old data rather than looking at the body of research as a whole.”
The WSJ could not confirm whether vaccines—which RFK Jr. and antivaccination proponents have long blamed for causing autism—will also be included in the HHS report. As things stand already, though, it seems unlikely that the HHS report will offer any real clarity of the complex causes of autism, as RFK Jr. has promised.
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