FILE PHOTO: U.S. President Donald Trump looks on as he sits, in the Oval Office at the White House in Washington, D.C., U.S., September 19, 2025. REUTERS/Ken Cedeno/File Photo

By Michael Erman

WASHINGTON (Reuters) -U.S. President Donald Trump is set to announce on Monday a link between the use of popular over-the-counter pain medication Tylenol and the development of autism during pregnancy, a claim which many doctors dispute.

Trump is also slated to suggest leucovorin, a form of folic acid, as a treatment for autism symptoms during a White House event. The Food and Drug Administration published a notice to the Federal Register on Monday approving a version of the drug made by GSK but later withdrew it.

The Department of Health and Human Services declined to comment on the notice or its withdrawal.

$50 MILLION IN GRANTS MAY BE ANNOUNCED

The event will likely also include an announcement of the recipients of $50 million in National Institutes of Health grants to study the causes of autism, a source with knowledge of the project told Reuters. Sources had told Reuters the winners were expected to be named by the end of September.

U.S. Health Secretary Robert F. Kennedy Jr. has promised to find the cause of autism and has long suggested it is related to vaccines without scientific proof. He has also said it must be related to an environmental toxin.

Researchers say there is no firm evidence of a link between the use of Tylenol and autism. The British health regulator MHRA said on Monday there remains no evidence linking the use of paracetamol, the active ingredient in Tylenol which is known as acetaminophen in the United States, during pregnancy with autism and that it continues to recommend it for pain relief.

Leucovorin, used to treat some cancer patients on chemotherapy, has shown some promise in very small trials, but large, randomized trials are needed, experts said.

WHITE HOUSE DECLINES TO COMMENT ON DETAILS

"I would encourage everyone in this room to go into the four o'clock announcement with some critical thinking skills and with some open ears to actually listen to what the president and his team of outsiders have to say about this," White House press secretary Karoline Leavitt told reporters at a briefing.

Shares of Tylenol manufacturer and consumer health company Kenvue were down 5.5% in trading Monday and have lost 17% in September as reports emerged that the administration would link the drug to autism.

Speaking to reporters on Sunday night, Trump said that he thinks the use of Tylenol is "a very big factor" in the rise of autism. The announcement could also link vaccines to the condition, Trump said.

"There's obviously something artificial that’s really wrong, and we think we know what that is," Trump said on Sunday.

STUDIES HAVE FAILED TO ESTABLISH CAUSE

Decades of studies have yet to establish a definitive cause, but many scientists believe genetics, potentially in combination with environmental influences, play a role.

Autism is a neurological and developmental condition marked by disruptions in brain signaling that cause people to behave, communicate, interact, and learn in atypical ways, according to the Centers for Disease Control and Prevention.

Tylenol is made by consumer health company Kenvue, which was spun off from Johnson & Johnson in 2023, and generic versions of acetaminophen are also available.

"We believe independent, sound science clearly shows that 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," Kenvue said in a statement.

Autism diagnoses in the United States have increased significantly since 2000, intensifying public concern. By 2020, the U.S. autism rate in 8-year-olds was 1 in 36, or 2.77%, up from 2.27% in 2018 and 0.66% in 2000, according to the CDC.

EXPERTS ARE STUDYING GENETIC LINKS

Many experts, including the CDC, have largely attributed the autism rate increase to widespread screening and the inclusion of a wider range of behaviors to define the condition, leading to the diagnosis of individuals with milder or more subtle signs of autism.

Kennedy has long suggested a link between vaccines and autism despite a lack of scientific evidence and has hired fellow vaccine critic David Geier to review long-established findings about vaccine safety data at the CDC.

Geier was fined by Maryland for practicing medicine without a license and prescribing dangerous treatments to autistic children.

ANTI-VACCINE GROUPS HAVE TRUMPETED TYLENOL LINK

Children's Health Defense, the anti-vaccine group formerly headed by Kennedy, has also focused on the link between Tylenol and autism.

Brian Hooker, chief scientific officer of CHD, has said he expects Kennedy to focus on Tylenol, as well as vaccines and vaccine components.

(Reporting by Michael Erman in New York, Julie Steenhuysen in Chicago, and Ahmed Aboulenein in Washington; Additional reporting by Nandita Bose, Jeff Mason, and Trevor Hunnicutt in Washington, Nancy Lapid in Tucson, and Sriparna Roy in Bengaluru; Editing by Caroline Humer)