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For nearly a decade, the immunologist and biochemist William Parker has tried, with little success, to persuade other scientists to take seriously his theory that acetaminophen—better known by the brand name Tylenol—is the primary cause of autism. Researchers have long failed to find a causal link between autism and any medication, and these days, most of them believe that a change in diagnostic criteria is largely behind the dramatic uptick in autism rates over the past 30 years. But late last month, Parker received a phone call from Health Secretary Robert F. Kennedy Jr., who wanted to learn more about his work. In fact, he’s heard from Kennedy several times since then. Parker also spoke recently with Jay Bhattacharya, the director of the National Institutes of Health. To hear Parker tell it, the nation’s top health officials have taken great interest in his ideas.
Over the past few weeks, Kennedy has reportedly been looking into an alleged connection between autism and Tylenol use during pregnancy. Parker’s preoccupation is slightly different: He believes that children’s use of Tylenol causes autism. Parker has for years operated on the fringes of academia. He runs his own small, independent laboratory, which he started after he lost a lab at Duke University’s medical school. (Duke did not renew Parker’s contract after he began focusing on autism in his research, though an email that an administrator sent to Parker in 2021, which I reviewed, said only that keeping the lab open wasn’t in his department’s “strategic best interest.”) Parker’s attempts to publish in academic journals have regularly been rebuffed. One reviewer tore into a recent submission from Parker, writing in their assessment that his hypothesis was “outrageous” and “illogical”; the paper was rejected. The past couple of weeks have been a wild reversal for Parker. “Nothing was happening and—boom!” he told me. “It’s beautiful.”
In April, Kennedy promised that Americans would know by September what causes autism and how to eliminate it. How exactly he would do that in five months was a mystery, especially considering that researchers have for decades tried to determine what genetic and environmental factors might be responsible. (Both seem likely to play a role, though studies have suggested that about 80 percent of a person’s autism risk is found in their DNA.) Kennedy had already brought in David Geier, a researcher who has published deeply flawed papers linking autism to vaccines, to uncover any irregularities in a CDC vaccine-safety database. Plus, Kennedy has a well-established history of anti-vaccine activism, and in particular of linking immunization to autism, despite reams of research indicating otherwise. He appeared poised to pin the blame for autism on childhood shots.
[Read: RFK Jr.’s autism time machine]
Last week, Laura Loomer, a far-right activist who seems to have a direct line to the White House, strongly hinted on X that Kennedy’s autism report, which has yet to be released, might implicate acetaminophen. A few days later, The Wall Street Journal, citing unnamed sources familiar with the discussions, also said that the report would likely link the drug to autism. Those stories focused on prenatal exposure to acetaminophen, which is considered the safest pain reliever and fever reducer available for pregnant women. In 2015, the FDA issued a tepid notice about the risks of using acetaminophen during pregnancy, mentioning conflicting results about a possible link to ADHD but nothing about autism. Since then, a handful of experts, including the dean of Harvard’s school of public health, have published papers suggesting an association between prenatal use of acetaminophen and neurodevelopmental disorders, including autism.
A spokesperson for Kenvue, the company that makes Tylenol, told me in an email, “We have evaluated available science and continue to believe that there is no link between acetaminophen use and autism.” (The spokesperson also noted that Parker has consulted in an ongoing lawsuit over cases of ADHD and autism allegedly caused by Tylenol use during pregnancy. Parker told me that he did offer consultation, but he didn’t testify in the case and didn’t accept any compensation—“not even a penny.”) The email also cited an FDA fact sheet, updated last month, that notes the agency has not found clear evidence of any harms of acetaminophen use during pregnancy.
Parker’s theory is that giving acetaminophen to babies and young children, not pregnant women, is what’s behind nearly all cases of autism. For more than an hour, he walked me through his research, citing studies that show how acetaminophen alters cognition in male mice, highlighting the increase in children’s use of the drug once aspirin stopped being recommended for them in the 1980s, and referencing a 2008 study led by an epidemiologist who believed that his son’s autism was caused by the acetaminophen he was given after getting an MMR shot.
[Read: Life before the measles vaccine]
Considering that the large majority of children receive acetaminophen—one study found that 95 percent of infants are given the drug at least once in their first year of life—acetaminophen alone clearly doesn’t cause autism. Parker contends that a constellation of factors, including genetics, inflammation, and stress, enable acetaminophen to trigger autism in certain children. In his first paper on the topic, published in 2017, he and his co-authors couched their words carefully, maintaining that it was “one explanation for the increased prevalence of autism.”
In the years since that paper’s publication, Parker has grown more confident. He now sees acetaminophen as the only possible explanation for the rising number of autism cases. When I asked him how certain he was of his conclusion, Parker told me, “We’ve thought about this a lot and it’s 99.99” percent. The only way he sees to increase that certainty to 100 percent is to stop giving American children acetaminophen. When that occurs, Parker told me, the number of autism cases will drop by about 95 percent and the remainder will likely be reclassified as some other disorder. He claims that autism, as we know it, will essentially end. When I asked Jeffrey Morris, a biostatistics professor at the University of Pennsylvania, about Parker’s prediction, he replied that “bold claims require rigorous, reproducible evidence”—and so far, judging by the response from fellow scientists, Parker hasn’t met that standard.
Parker acknowledges that his work has not been embraced by mainstream autism researchers. Viktor Ahlqvist, the author of a 2024 Swedish study that concluded that acetaminophen use during pregnancy was not associated with autism, told me that developmental outcomes in early life are “notoriously difficult to study,” and that many apparent correlations—say, acetaminophen use and autism—don’t hold up to scrutiny. When I asked Parker to give me the names of scientists who support his theory, he couldn’t think of anyone. (He said Kennedy asked him for names too.) I contacted several longtime autism researchers, none of whom had heard of Parker. His 2023 paper trumpeting the dangers of acetaminophen has been cited a mere 11 times, according to Google Scholar. (By contrast, a 2007 paper Parker wrote on beneficial bacteria in the appendix has been cited 500 times.) For someone who is 99.99 percent certain he knows what causes autism and how to end it, Parker has hardly made a mark.
And yet, American health officials appear to have sought his advice anyway. Parker showed me screenshots of emails arranging a Zoom between him and Bhattacharya, as well as a document he emailed to Bhattacharya’s assistant summarizing his research findings. (According to Parker, on their Zoom call, Bhattacharya said Parker had given him a lot of homework and he would be in touch.) Parker also shared his call log, which included five calls with Kennedy. (The Atlantic verified that the phone number is in fact Kennedy’s.) On Sunday, I asked Parker when he had last spoken with Kennedy. “What time is it now?” he said. Kennedy had called a few hours earlier—Parker told me he’d wanted to discuss the Swedish study. A spokesperson for Health and Human Services declined to say whether Kennedy or Bhattacharya had spoken with Parker. “We are using gold-standard science to get to the bottom of America’s unprecedented rise in autism rates,” the spokesperson wrote in an email. “Until we release the final report, any claims about its contents are nothing more than speculation.”
[Read: ‘This is not how we do science, ever’]
For Kennedy, the allure of Parker’s theory seems obvious. The secretary has not only pledged to find out the causes of autism but also stressed that the Trump administration will be able to eliminate them. Parker supplies a ready solution that nicely dovetails with Kennedy’s hostility toward vaccines, and pharmaceutical interventions against disease in general. Parker isn’t claiming that vaccines cause autism, but according to his theory, they could lead to the stress and inflammation that create the environment for what he insists is the true trigger.
Four days after Kennedy first called Parker, at an August 26 Cabinet meeting, Trump asked his health secretary to provide an update on his promise to discover the cause of autism. Kennedy told the president that he had found “certain interventions now that are clearly, almost certainly causing autism.” Trump, who likes to hint at insider secrets, chimed in that there “has to be something artificially causing this, meaning a drug or something.” Parker took that exchange as a sign that his research might have finally found a sympathetic audience.