President Trump revealed at Charlie Kirk's memorial at State Farm Stadium outside Phoenix, Arizona, on Sunday afternoon that the "biggest medical announcement in U.S. history" will be announced on Monday, adding, "I think we've found an answer to autism."

JUST IN - Trump says tomorrow will be the "biggest announcement medically" in the history of U.S., "I think we've found an answer to autism." pic.twitter.com/e1WrejfsfH

— Disclose.tv (@disclosetv) September 21, 2025

Hours later, The Washington Post reports that Trump administration officials, including Health Secretary Robert F. Kennedy Jr., plan a press conference later today to warn pregnant women against using acetaminophen, the active ingredient in Tylenol, over alleged links to autism. 

The new guidance from HHS follows a series of lawsuits alleging that Tylenol use during pregnancy caused autism. A federal judge rejected these claims in 2023, citing flawed science, and a 2024 Swedish study of 2.5 million siblings found no increased autism risk tied to prenatal acetaminophen use.

Tylenol-maker Kenvue disputed the Trump administration's new guidance, citing a decade of independent research and global health regulators that found no concrete evidence of such a link.

Kenvue told Bloomberg on Sunday that "independent, sound science" shows taking acetaminophen does not cause autism.

"We strongly disagree with any suggestion otherwise and are deeply concerned with the health risk this poses for expecting mothers," the company said in a statement, adding, "The facts are that over a decade of rigorous research, endorsed by leading medical professionals and global health regulators, confirms there is no credible evidence linking acetaminophen to autism."

Shares of Kenvue were down 4% in premarket trading on the news. 

Goldman analyst Esah Hayat told clients earlier, "Trump administration plans to link the active ingredient in Tylenol to autism today according to the Washington Post. Some have suggested that there could be knock-on effects to paracetamol usage outside of the US among pregnant women, noting that a lot of agencies tend to be led by FDA recommendations. That said, there have been a lot of studies on this topic in the past and no causal link has been found to date. Not a hugely worrying headline as we're (unfortunately) used to this new baseline of regulatory vol but could see some consumer health weakness through the day."

At the start of the month, the Wall Street Journal reported that RFK. Jr. would soon release a report connecting the painkiller acetaminophen during pregnancy to autism. 

WSJ also noted that the Trump administration will suggest other potential causes of autism and suggest further study. It's not yet certain whether certain vaccines will be mentioned later today. 

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