“Sideshow”

Anti-vaccine groups melt down over RFK Jr. linking autism to Tylenol

“THIS WAS NOT CAUSED BY TYLENOL” Kennedy’s anti-vaccine group retweeted.

Beth Mole – Sep 22, 2025 6:05 pm | 467

Health and Human Services Secretary Robert Kennedy Jr. appears before the Senate Finance Committee at the Dirksen Senate Office Building on September 4, 2025 in Washington, DC. Credit: Getty | Andrew Harnik

Health Secretary and anti-vaccine activist Robert F. Kennedy Jr. on Monday evening announced that the use of Tylenol (aka acetaminophen, paracetamol) during pregnancy is linked to autism—an unproven assertion that had previously sent Kennedy’s anti-vaccine allies into a rage.

In a press event alongside Trump, Kennedy said that the Food and Drug Administration will work to update the drug’s safety label and notify physicians of the concerns. At the same time, the administration also touted leucovorin (folinic acid) as a potential treatment for autism, though there is scant evidence behind its use for autism.

Before the announcement, news reports revealing Kennedy’s plan angered his anti-vaccine followers.

“We didn’t wait 20 years for Bobby to finally speak and then get served Tylenol as an answer,” anti-vaccine group Georgia Coalition for Vaccine Choice wrote in an unhinged Facebook post on Monday morning. “If that’s all we hear – is that the end? Not thimerosal. Not aluminum. Not MMR. Not Hep B. Not the insane schedule pushed after pharma got liability protection. Are we supposed to just forget?”

Children’s Health Defense (CHD)—the anti-vaccine group founded by Kennedy—even got in on the backlash, retweeting a post on Monday about parents who falsely blame vaccines for their children’s neurological condition, with the statement: “THIS WAS NOT CAUSED BY TYLENOL.”

Kennedy’s effort to link Tylenol to autism was first reported earlier this month by The Wall Street Journal. However, fury erupted again after President Trump mentioned in a speech Saturday that there would be a “big announcement” on the cause of autism on Monday. Then, on Sunday, The Washington Post reported that the announcement Trump was referring to was the report linking autism to the use of acetaminophen during pregnancy.

In past years, CHD has fear-mongered that children’s use of Tylenol early in life (not in pregnancy) may be a cause of autism. But the organization has been tepid at best on Kennedy’s effort to link use in pregnancy to autism.

In an interview on Steve Bannon’s podcast War Room on Monday, CHD President Mary Holland downplayed the link, telling Bannon: “Today may be something of a sideshow—Tylenol is not the primary cause. Vaccines are the primary cause [of autism],” Holland said. (The claim that vaccines cause autism has been thoroughly and repeatedly debunked.)

Bannon, for his part, slammed Kennedy’s effectiveness as health secretary, calling his efforts to implement an anti-vaccine agenda unserious and amateurish. “This Tylenol thing stinks to high heaven,” he said.

No clear link between Tylenol and autism

The alleged link between Tylenol use during pregnancy and the development of autism is not entirely bunkum, but it also is far from proven. The scientific literature on the topic has been mixed, with some studies finding a possible association and others not finding one.

In August, a literature review in BMC Environmental Health led by a Harvard researcher reexamined data from 46 previously published studies and concluded that use of Tylenol early during pregnancy appeared to be associated with a higher risk of neurodevelopmental disorders, including autism. But, it’s worth noting that many studies on the topic have significant limitations and don’t account for important factors, including genetic factors. It’s also important to note that the Harvard researcher behind that literature review served as an expert witness for a plaintiff’s legal team in a case claiming links between acetaminophen use during pregnancy and neurodevelopmental disorders.

Many medical experts, instead, point to a novel 2024 study conducted in Sweden. The study, published in JAMA, used data from a population of 2.5 million children and was also able to compare differences among (full) siblings. This provided a simple way to skirt confounding variables, such as genetics and environmental factors, to which siblings would have similar exposure.

In the entire population, children exposed to acetaminophen during pregnancy were slightly more likely to be diagnosed with autism than those who weren’t—echoing some earlier studies. But, in the sibling analysis, which compared siblings who were exposed to acetaminophen to siblings who were not, the association vanished. In all, the data suggests that acetaminophen was not causing an uptick in autism diagnoses; rather, there were other confounding factors behind the link. The authors explain:

Results of this study indicate that the association between acetaminophen use during pregnancy and neurodevelopmental disorders is a noncausal association. Birthing parents with higher acetaminophen use differed in many aspects from those with lower use or no use. Results suggested that there was not one single “smoking gun” confounder, but rather that multiple birthing parents’ health and sociodemographic characteristics each explained at least part of the apparent association. The null results of the sibling control analyses indicate that shared familial confounders were involved, but do not identify the specific confounding factors.

Critical factors

Another factor to consider is that untreated fevers, and/or prolonged fevers during pregnancy—reasons to take Tylenol in the first place—are linked to increased risks of autism. And, as the Society for Maternal-Fetal Medicine pointed out earlier this month, untreated fever and pain during pregnancy carry other significant risks for both the mother and the pregnancy.

“Untreated fever, particularly in the first trimester, increases the risk of miscarriage, birth defects, and premature birth, and untreated pain can lead to maternal depression, anxiety, and high blood pressure,” SMFM noted.

With no clear evidence supporting a link between acetaminophen and autism, doctors highlight another fold in the issue: Acetaminophen is considered the safest pain reliever/fever-reducer during pregnancy. Nonsteroidal anti-inflammatory medications (also called NSAIDS), such as ibuprofen (Advil) and aspirin, can cause reduced blood flow, heart problems, and kidney problems in a fetus.

After The Wall Street Journal’s report of Kennedy’s plans, the American College of Obstetricians and Gynecologists (ACOG) reiterated its guidance for acetaminophen during pregnancy, writing on social media:

Acetaminophen remains a safe, trusted option for pain relief during pregnancy. Despite recent unfounded claims, there’s no clear evidence linking prudent use to issues with fetal development. ACOG’s guidance remains the same. When pain relief is needed during pregnancy, acetaminophen should be used in moderation, and after consulting your doctor.

Christopher Zahn, ACOG’s chief of clinical practice, put it more plainly, saying: “Pregnant patients should not be frightened away from the many benefits of acetaminophen, which is safe and one of the few options pregnant people have for pain relief.”

This post has been updated to include the announcement and to correct the number of studies in the BMC Environmental Health review.

Beth Mole Senior Health Reporter

Beth is Ars Technica’s Senior Health Reporter. Beth has a Ph.D. in microbiology from the University of North Carolina at Chapel Hill and attended the Science Communication program at the University of California, Santa Cruz. She specializes in covering infectious diseases, public health, and microbes.

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