In September, Secretary of Health and Human Services Robert F. Kennedy Jr. delivered on his earlier promise of naming a cause of autism. This announcement came in the form of an X post and a press conference, rather than as a peer-reviewed and scientifically rigorous report. In it, he claimed that autism is linked to Tylenol use during pregnancy, an idea that has been previously investigated and disproven.

While some studies may suggest a link between the two, these studies, by nature, cannot be perfectly controlled or random. Fevers pose an immense risk to pregnant people, and not using Tylenol would leave them untreated and discomfortable. Instead, these conclusions were observational studies, which lack control or analysis of additional variables such as environment or genetics. This makes the proposed link tentative at best. 

Additionally, a recent study that compared siblings—where one sibling had been exposed to Tylenol during pregnancy, and the other had not—resulted in the link disappearing altogether. Since siblings largely share any confounding factors, the study reduced additional variables and was able to more definitively examine the proposed connection. It ultimately concluded that the Tylenol-autism link present in non-sibling studies is one of correlation, not causation. In other words, it found that Tylenol does not cause autism.

This evidence has not stopped Kennedy, however, who has only doubled down with increasingly bizarre allegations. In a cabinet meeting on October 9th, Kennedy presented an entirely unrelated claim, asserting that “There are two studies that show children who are circumcised early have double the rate of autism. It’s highly likely because they’re given Tylenol.” 

There is virtually no basis for the claim that giving young children Tylenol causes autism. Of the two studies Kennedy cited, neither actually measured Tylenol intake, and his other source, a pre-print (meaning it has been peer-reviewed or accepted to any scientific journals), is focused not on any new evidence of a possible link. Instead, it seeks “To understand why the conclusions [that Tylenol causes autism in children] have not been widely accepted”, which makes it, at best, an incredibly biased review. Basing a sweeping proclamation off of any of these sources is highly questionable, and Kennedy has once again spread disinformation using his position as HHS Secretary.