By Berkeley Lovelace Jr., Aria Bendix and Erika EdwardsPresident Donald Trump said Monday the Food and Drug Administration approved a chemotherapy drug called leucovorin as a treatment to alleviate symptoms of autism, despite little evidence that the medication works.Trump also said the administration is issuing a warning to doctors not to recommend acetaminophen — the active ingredient in Tylenol and other widely used medications — for pregnant women, claiming it may be linked to autism in children. Trump had been teasing the announcement for days, as Health Secretary Robert F. Kennedy Jr. and other health officials have pledged to determine the cause of the developmental disorder by September.The administration had planned to release its long-awaited report on causes of autism around Sept. 29 or Sept. 30, a person familiar with the matter told NBC News. But Trump pre-empted the rollout over the weekend, and details soon appeared in The Washington Post.“We understood a lot more than a lot of people who studied it,” Trump said from the White House, referring to autism. He spoke alongside Kennedy, Food and Drug Administration Commissioner Marty Makary, National Institutes of Health Director Jay Bhattacharya and Mehmet Oz, administrator of the Centers for Medicare and Medicaid Services. ”Taking Tylenol is not good,” Trump said. “I’ll say it. It’s not good.”Leucovorin is a drug approved by the FDA to counteract the side effects of certain chemotherapy drugs and sometimes used off-label to treat vitamin B9 deficiency. Leucovorin is a form of folinic acid, a B vitamin. It has shown promise in clinical trials with helping some children with autism improve their speech. But the Autism Science Foundation, which funds evidence-based autism research, does not recommend it as a treatment yet and says more studies are needed.Trump said the FDA updated the drug’s label Monday for the treatment of autism symptoms. Oz said Medicaid — in partnership with states — will cover it with a prescription.“We believe insurance companies will rapidly follow our lead,” he said.Kennedy also said the FDA will issue a letter advising health care providers that the over-the-counter medication should be used during pregnancy only in cases of high fever, when the fever itself may pose a health risk to the fetus. The FDA’s notice, sometimes called a “Dear Doctor” letter, is meant to alert physicians and other prescribers about urgent or clinically significant safety issues it has identified with a drug. Kennedy also said the FDA will begin the process to initiate a safety label change for the drug.Bhattacharya said at Monday’s briefing that the NIH will dedicate $50 million to 13 research projects focused on identifying root causes and treatments for autism, an effort known as the “autism data science initiative.” The research will focus on environmental and medical factors, nutrition, events during pregnancy, biology and genetics, he said.“Given this wide range of symptoms across the spectrum, it seems certain that there will be a wide range of biological contributors to explaining the cause,” he said.Researchers who’ve spent decades researching potential causes of autism say the administration hasn’t uncovered any new evidence — and the existing data still doesn’t support its claims.“This is not new,” Dr. Allison Bryant, a high-risk obstetrician at Massachusetts General Hospital in Boston, said in an earlier interview. “It has bubbled up every now and again with studies that show maybe some kind of association but not clearly showing any cause and effect.”Experts say autism spectrum disorder, which is characterized by challenges with social and speech skills and by repetitive behaviors, most likely stems from multiple factors rather than a single cause. It affects 1 in 31 children in the United States, according to the Centers for Disease Control and Prevention.The bulk of scientific research hasn’t identified a link between acetaminophen and autism.“The science hasn’t changed regardless of what comes out from the report,” said Brian K. Lee, a professor of epidemiology at Drexel University in Philadelphia, referring to the Trump administration’s finding. “I’m not sure what the administration is doing, but it looks like they’re just going back and reviewing the evidence and they’re coming to a different conclusion than many scientists would.”Acetaminophen was introduced in the United States in the 1950s as a prescription alternative to aspirin. By the 1970s, it had been made available over the counter and became one of the most commonly used pain and fever medications in the country. The American College of Obstetricians and Gynecologists and other major medical groups say acetaminophen is one of the only safe pain relievers for women during pregnancy, and studies have shown no clear evidence that use during pregnancy leads to developmental issues in kids. The drug is also found in name brands like Theraflu and Excedrin.Forty percent to 65% of women use acetaminophen at some point during pregnancy, according to a 2014 study published in the American Family Physician.Earlier Monday, White House press secretary Karoline Leavitt touted a “major announcement” from Trump, telling reporters at a briefing to go into the autism announcement with “some critical thinking skills and with some open ears.”“They are paying attention to studies, and the gold standard of science and research, that many in this city for far too long have turned a blind eye to,” she said.Trump administration officials are citing previous research, including a literature review Mount Sinai and Harvard researchers published last month in the journal BMC Environmental Health. The review concluded there was most likely an association between autism and acetaminophen exposure during pregnancy. Outside autism researchers, however, said that the review wasn’t rigorously conducted and that it cherry-picked studies that supported its conclusion. The review’s senior author, Andrea Baccarelli, served in 2023 as a paid expert in a class action lawsuit against acetaminophen manufacturers, in which he testified that there was a link between the medication and autism. A judge ultimately excluded his testimony for being scientifically unsound and last year dismissed the case, which is being appealed.Baccarelli said in a statement that he and his colleagues conducted a rigorous review and that the association with neurodevelopmental disorders was strongest when acetaminophen was taken for four weeks or longer. He said he discussed his findings with Kennedy and Bhattacharya in recent weeks.“Further research is needed to confirm the association and determine causality, but based on existing evidence, I believe that caution about acetaminophen use during pregnancy — especially heavy or prolonged use — is warranted,” Baccarelli said.However, other autism researchers have pointed to a large study last year published in the Journal of the American Medical Association, which found no link between acetaminophen use in pregnancy and autism, ADHD or intellectual disability. The study, from Lee and his colleagues in Sweden, analyzed data from more than 2.4 million children. When the researchers looked solely at children with autism, there was a small increased risk possibly associated with acetaminophen. But when the researchers compared siblings within the same families — one exposed during pregnancy, the other not — the link disappeared. The comparison allowed them to control for variables that past studies couldn’t. Siblings share a large part of their genetic background and often have similar environmental exposures in utero and at home.“The biggest elephant in the room here is genetics,” Lee said. “We know that autism, ADHD and other neurodevelopmental disorders are highly heritable.”In an emailed statement, a spokesperson for Kenvue, the maker of Tylenol, said the drug is the safest pain reliever option for pregnant women.“Without it, women face dangerous choices: suffer through conditions like fever that are potentially harmful to both mom and baby or use riskier alternatives,” the spokesperson said. “We believe independent, sound science clearly shows that taking acetaminophen does not cause autism.”Bryant, of Massachusetts General Hospital, said, “The best science that we have available would still suggest that acetaminophen is a safe pain reliever and fever reducer in pregnancy.”Berkeley Lovelace Jr.Berkeley Lovelace Jr. is a health and medical reporter for NBC News. He covers the Food and Drug Administration, with a special focus on Covid vaccines, prescription drug pricing and health care. He previously covered the biotech and pharmaceutical industry with CNBC.Aria BendixAria Bendix is the breaking health reporter for NBC News Digital.Erika EdwardsErika Edwards is a health and medical news writer and reporter for NBC News and “TODAY.”