“Don’t take Tylenol,” Trump instructed pregnant women around a dozen times during the unwieldy White House news conference, also urging mothers not to give their infants the drug, known by the generic name acetaminophen in the U.S. or paracetamol in most other countries. He also fueled long-debunked claims that ingredients in vaccines or timing shots close together could contribute to rising rates of autism in the U.S., without providing any medical evidence.

The rambling announcement, which appeared to rely on existing studies rather than significant new research, comes as the Make America Healthy Again movement has been pushing for answers on the causes of autism. The diverse coalition of supporters of Health Secretary Robert Kennedy Jr. includes several anti-vaccine activists who have long spread debunked claims that immunizations are responsible.

The announcement also sheds light on Trump’s own long-held fascination with autism and his trepidation about the childhood vaccine schedule, even as the president has taken pride in his work to disseminate COVID-19 vaccines during his first term.

Medical experts said Trump’s remarks were irresponsible. New York University bioethicist Art Caplan said it was “the saddest display of a lack of evidence, rumors, recycling old myths, lousy advice, outright lies, and dangerous advice I have ever witnessed by anyone in authority.”

Trump announced during the event that the Food and Drug Administration would begin notifying doctors that the use of acetaminophen “can be associated” with an increased risk of autism, but did not immediately provide justification for the new recommendation.

Evidence for potential link between Tylenol and autism is not conclusive

Some studies have raised the possibility that taking acetaminophen during pregnancy might increase the risk of autism — but many others haven’t found that concern, said autism expert David Mandell of the University of Pennsylvania.

One challenge is that it’s hard to disentangle the effects of Tylenol use from the effects of high fevers during pregnancy. Fevers, especially in the first trimester, can increase the risk for miscarriages, preterm birth and other problems, according to the Society for Maternal-Fetal Medicine.

Trump also urged not giving Tylenol to young children, but scientists say that research indicates autism develops in the fetal brain.

Responding to Trump’s warnings, the Society for Maternal-Fetal Medicine said they still recommend Tylenol as an appropriate option to treat fever and pain during pregnancy. The president of the American College of Obstetricians and Gynecologists said Monday that suggestions that Tylenol use in pregnancy causes autism are “irresponsible when considering the harmful and confusing message they send to pregnant patients.”

Trump press secretary Karoline Leavitt said in a statement Monday evening that the administration “does not believe popping more pills is always the answer for better health” and that it “will not be deterred in these efforts as we know millions across America are grateful.”

Tylenol maker Kenvue disputed any link between the drug and autism on Monday and said in a statement that if pregnant mothers don’t use Tylenol when in need, they could face a dangerous choice between suffering fevers or using riskier painkiller alternatives. Shares of Kenvue Inc. fell 7.5% in trading Monday, reducing the company’s market value by about $2.6 billion.

Kennedy announced during the news conference that at Trump’s urging, he was launching a new all-agency effort to uncover all the factors that could be contributing to autism, a question scientists have been researching for decades.

Trump administration explores the potential role of folate

FDA Commissioner Dr. Marty Makary also took the stage to announce it was taking the first steps to try to approve a folic acid metabolite called leucovorin as a treatment option for patients believed to have low levels of folate in the brain. That may include some people with autism.

Leucovorin is used to counteract the side effects of various prescription drugs, including chemotherapy and other high-dose medications that can negatively impact the immune system. It works by boosting folate levels, a form of vitamin B that’s critical to the body’s production of healthy red blood cells.

Women already are told to take folic acid before conception and during pregnancy because it reduces the chances of certain birth defects known as neural tube defects.

In recent years a handful of studies have suggested positive results when high-dose folic acid is used to treat children with autism, with researchers in China and other countries reporting improvements in social skills and other metrics. Those small studies have been quickly embraced by some parts of the autism community online.

The theory is that some, not all, children with autism may not properly metabolize folate, Mandell said. But the recent studies “are really tiny,” he said. To prove an effect, “we would need an independent, large, rigorously controlled randomized trial.”

Decades of studies show no link between vaccines and autism

During the press conference, Trump said he’s a believer in vaccines but claimed without evidence that giving vaccinations close together at the recommended ages has a link to autism. Spacing out shots as he suggests can lead to an increased risk that children become infected with a vaccine-preventable disease before returning for another visit.

Though anti-vaccine activists, including Kennedy, have long suggested a link between vaccines and autism, widespread scientific consensus and decades of studies have firmly concluded there isn’t one.

Autism is not a disease but a complex developmental condition that affects different people in different ways. It can include delays in language, learning or social and emotional skills. For some people, profound autism means being nonverbal and having intellectual disabilities, but the vast majority of people with autism experience far milder effects.

The disorder affects 1 in 31 U.S. children today, a sharp rise from just a few years ago, according to the CDC. Experts say the increase is mainly due to a new definition for the disorder that now includes mild cases on a “spectrum” and better diagnoses. They say there is no single cause to the disorder and say the rhetoric appears to ignore and undermine decades of science into the genetic and environmental factors that can play a role.

The announcement is the latest step the administration, driven by Kennedy and his supporters, has taken to reshape America’s public health landscape.

Beyond cutbacks at federal health agencies, the Centers for Disease Control and Prevention has been roiled by disagreements over Kennedy’s vaccine policies. An influential immunization panel stocked by Kennedy with figures who have been critical of vaccines last week changed shot guidance for COVID-19 and other diseases.

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Swenson reported from New York. Associated Press writers Matthew Perrone and Laura Ungar contributed to this report.