News reports have indicated Health and Human Services Secretary Robert F. Kennedy Jr. may point to Tylenol and folate deficiency in his promised announcement on the causes of autism. But neither Tylenol nor folate deficiency has been shown to cause autism. Some evidence has pointed away from Tylenol as a risk factor.
“By September, we will know what has caused the autism epidemic, and we’ll be able to eliminate those exposures,” Kennedy said in an April 10 Cabinet meeting. In an Aug. 26 Cabinet meeting, Kennedy said that the administration will “have announcements, as promised, in September. We’re finding interventions, certain interventions now, that are clearly, almost certainly causing autism.”
On Sept. 5, the Wall Street Journal reported that Kennedy would suggest a connection between autism and use of Tylenol, or acetaminophen, during pregnancy, based on conversations about an expected HHS autism report with “people familiar with the matter.” As we will discuss below, Tylenol hasn’t been shown to cause autism, and some experts told us that the best current evidence points away from this conclusion. Failing to treat fever and pain in pregnancy can be dangerous for the mother and infant.
Others had previously speculated on a role for Tylenol in the autism report.
“ATTENTION TO EVERYONE WHO HAS EVER TAKEN TYLENOL OR KNOWS SOMEONE WITH AUTISM,” conservative activist Laura Loomer posted Sept. 2 on X, accompanying her text with police car light emojis. “Link Between Prenatal Tylenol @tylenol Use and Autism Rates Under Scrutiny as @HHSGov Prepares Major September Announcement On Autism Interventions.”
Dr. Robert Malone, one of the new members Kennedy appointed to the Centers for Disease Control and Prevention’s vaccine advisory committee, predicted that same day that Kennedy’s announcement might link autism to a combination of Tylenol use and vaccination in very young children. There isn’t evidence to support that. Malone, who has a history of making inaccurate claims about vaccines, made his comments on a show hosted by former member of Congress Matt Gaetz.
The Wall Street Journal article also said the report would suggest some role for low levels of the vitamin folate in autism and that folinic acid could be used to treat autism symptoms. Some research has indicated that taking folic acid — another form of folate already recommended for women who could become pregnant — is associated with a lower likelihood of having a child with autism. However, it remains unclear whether the vitamin is causing the reduced autism risk. Experts told us the evidence on folinic acid as an autism treatment is very limited.
HHS officials have not given details on the planned content of the report. In a Sept. 8 appearance on Bloomberg TV, Food and Drug Administration Commissioner Dr. Marty Makary called the Wall Street Journal’s reporting “premature,” stating that the report had not yet been written.
“We are using gold-standard science to get to the bottom of America’s unprecedented rise in autism rates,” an HHS spokesperson told us via email. “Until we release the final report, any claims about its contents are nothing more than speculation.”
Central to Kennedy’s promises on autism has been the idea that the increasing autism rate is caused by some “environmental toxin” that he can find and eliminate, as Kennedy has said.
As we have written previously, there is evidence that changes in diagnostic criteria, screening, services and awareness of the condition have affected how many cases of autism are diagnosed. There may have been some true increase in autism over several decades, but if so, it is far less dramatic than Kennedy has made it out to be. Genetics plays a major role in autism risk.
“There is no one cause of autism,” Rebecca Schmidt, a molecular epidemiologist and autism researcher at the University of California, Davis, and the school’s MIND Institute, told us, explaining that the condition most likely results from a combination of genetic and environmental risk factors that interact with one another. “It’s just likely to be a complex mixture of things that happen at the right times that lead to having a diagnosis of autism later,” she said, adding that these factors might be different for different people. Environmental risk factors can include exposures to particular substances but also factors such as maternal health conditions or infections during pregnancy.
Tylenol During Pregnancy Not Shown to Cause Autism
There have been some studies showing an association between the use of acetaminophen during pregnancy and having a child with autism or attention-deficit/hyperactivity disorder, leading to concerns and lawsuits. As we have written before, there are many other factors that could explain this. A federal judge ruled in 2023 that the evidence backing a mass lawsuit against the drugs was not strong enough to be admissible, and some recent studies that have tried to disentangle the issue have further cast doubt on the link.
“As far as the evidence goes, it points towards no causal association between acetaminophen use during pregnancy and risk of neurodevelopmental disorders, including autism,” Brian Lee, a professor of epidemiology at Drexel University’s Dornsife School of Public Health, told us.
Lee was a co-author of a study of nearly 2.5 million Swedish children published last year that, like some other studies, found an association between acetaminophen use during pregnancy and a slightly increased risk of neurodevelopmental disorders. But the researchers found that other factors, not acetaminophen, were likely responsible for that finding. When the researchers compared siblings to better control for various factors, the association with acetaminophen disappeared. The results suggest that acetaminophen is not causing autism, and that the observed associations are spurious.
Members of the Coalition for Autism Scientists wrote in a statement, posted online in response to the Wall Street Journal article, that studies assessing whether acetaminophen plays a role in autism are “difficult to conduct.” The coalition of more than 250 U.S. researchers was formed this year to push back against inaccurate claims from HHS about autism, as well as to monitor government autism research efforts. The studies that have found a connection “do not do a good job” of disentangling use of acetaminophen from the reasons women use it, they said.
For example, mothers with more genetic risk for neurodevelopmental disorders like autism and ADHD report more pregnancy pain, headaches and migraines and are more likely to use acetaminophen, Lee said. So a mother’s genetics may both cause her to take more acetaminophen and make it more likely that she will have a child with a neurodevelopmental disorder.
“In stronger studies, especially those that compare siblings within the same family, the link usually disappears. We also don’t see the kind of clear, repeatable patterns you’d expect if acetaminophen were truly the cause” of autism, Dr. Sura Alwan, a clinical teratologist at the University of British Columbia and executive director for PEAR-Net Society, a nonprofit focused on maternal-fetal development, told us in an email. “So, the most likely explanation is that other factors — like why someone needed acetaminophen in the first place, family genetics, or how the data were collected — are driving those results.”
Loomer’s X post embedded Fox News coverage of an Aug. 14 review study on acetaminophen and neurodevelopmental disorders, which concluded the evidence was “consistent with an association” and pregnant women should be advised to “limit acetaminophen consumption.” But the authors told news outlets that their review did not establish a causal link.
A new Japanese study, published Sept. 2, showed an association between acetaminophen during pregnancy and increased risk of neurodevelopmental conditions that went away in a sibling analysis.
“When you add these bits and pieces together — with our Swedish study having similar results with this Japanese study — I think the evidence points even further away from any possible causal link between acetaminophen and autism and ADHD,” Lee said.
He added that he wasn’t advocating to “completely close the chapter on acetaminophen,” but rather said that someone seeking to claim a causal link between the drug and autism will need to confront evidence to the contrary. He said that the medication has known risks, such as liver toxicity and overdose, if not used according to recommendations.
The American College of Obstetricians and Gynecologists has long recommended that people take acetaminophen only as needed and in consultation with a doctor, while pointing out that people have very limited safe options for pain relief during pregnancy.
“There is no clear evidence that proves a direct relationship between the prudent use of acetaminophen during pregnancy and fetal developmental issues,” Dr. Christopher Zahn, ACOG’s chief of clinical practice, said in a statement provided to us. He added that failing to take acetaminophen when indicated “is, at present, understood to be far more dangerous than theoretical concerns based on inconclusive reviews of conflicting science.”
“Pregnant patients can be reassured that using acetaminophen to treat pain and fever is safe,” a Sept. 5 statement from the Society for Maternal-Fetal Medicine said. “Untreated fever, particularly in the first trimester, increases the risk of miscarriage, birth defects, and premature birth, and untreated pain can lead to maternal depression, anxiety, and high blood pressure,” the statement also said.
“The biggest risk is that pregnant people might stop treating fevers or severe pain out of fear,” Alwan said, when asked about the practical consequences of promoting a poorly supported link between acetaminophen and autism. She also suggested that some mothers might instead take other types of pain medication, such as opioids or NSAIDS, “which carry clearer and more serious risks in pregnancy.”
Unfounded Claims About Tylenol and Vaccines
Also in recent weeks, people and organizations with a history of spreading anti-vaccine misinformation have been making unfounded claims about a link between Tylenol, vaccines and autism.
“I speculate that what we might hear is something about the interaction of Tylenol in the very young together with things that are pro-inflammatory, like say, for example, multiple vaccination,” Malone, the doctor on Kennedy’s vaccine advisory committee, said in his Sept. 2 “Matt Gaetz Show” appearance. “That may be part of the issue associated with autism.”
Children’s Health Defense, a nonprofit Kennedy founded that has long spread falsehoods about vaccines, also raised the idea that Tylenol combined with childhood vaccines causes autism in a Sept. 5 article, linking to a 2008 study.
But Lee, the autism researcher from Drexel, told us in an email that there are “a lot of problems with the paper,” which, based on parent surveys, found an association between acetaminophen use after the measles, mumps and rubella, or MMR, vaccine and autism.
Among other issues, the researchers recruited study participants non-randomly, “targeting an autism-aware population on the internet that is seeking answers to what is causing their child’s condition,” Lee said. The participants were asked to remember whether their children received acetaminophen after vaccinations, on average six to seven years prior. The study was also done at a time when participants may have heard claims based on another study — which was later found to be fraudulent — that the MMR vaccine caused autism. Lee suggested that these factors could have biased the results.
Furthermore, he said, even if the study did not have these issues, there could have been some explanation for the results that didn’t involve the medication causing autism. “A more parsimonious and biological evidence-supported interpretation of the data would be that undiagnosed autism is associated with differential health and or immune response that leads to acetaminophen use,” he said.
“There’s simply no credible science behind the idea that acetaminophen after vaccination causes autism,” Alwan said.
Prenatal Folic Acid
The Wall Street Journal article also suggested the HHS autism report would mention folate deficiency as a possible autism cause. It’s unclear what the report will say, but there is some support for the idea that folic acid supplementation around the beginning of pregnancy is linked to a reduced rate of autism in children. However, it hasn’t been established that prenatal folic acid reduces autism risk.
Furthermore, the current evidence doesn’t support any new recommendation, since pregnant women are already recommended to take folic acid. “There’s more plausibility with the folate story than there is with acetaminophen right now, but certainly more research is needed,” Lee said, referring to the evidence on folic acid during pregnancy. But he added that “if this does turn out to be concrete and true, I don’t think it would really change current practice.”
Folic acid is a synthetic form of folate, a type of B vitamin essential for many cellular functions, including those important for development of the nervous system. The U.S. began fortifying some grains with folic acid in 1998 to prevent neural tube defects, or problems with the brain and spine that occur when the neural tube does not close properly during the first month or so of pregnancy. People also are advised to take folic acid supplements leading up to and during pregnancy.
Folate is also found naturally in foods, such as leafy green vegetables, avocados, beans and oranges, but it can be challenging to get the recommended amount during pregnancy just from nonfortified foods. Folate deficiency is uncommon in the U.S., and the rate of neural tube defects fell following the addition of folic acid to grains.
Schmidt, the UC Davis autism researcher, has been publishing research since the early 2010s on a potential link between greater folic acid intake around the beginning of pregnancy and decreased risk of autism in children. Subsequent research has continued to suggest this.
However, Schmidt said, that doesn’t mean it’s certain that taking folic acid in early pregnancy reduces the risk of having a child with autism. The studies showing this link are observational, meaning they collect information on the mother’s folic acid intake but do not randomly assign people to take folic acid or not.
“We don’t know if it’s causal,” Schmidt said. “The only way we’ll ever know if that’s a true causal association is if we do a randomized, double-blind, controlled study.” It is not considered ethical to randomly assign people to not receive folic acid, she said, but she has pondered a trial randomly assigning people to different doses of folic acid.
Lee pointed out that a challenge of nutritional epidemiology research is that nutrients “tend to travel in packs.” People who are consuming enough folate likely also are consuming more healthy things in general. And they are also more likely to be engaging in other healthy behaviors, such as exercising and sleeping well. “So when you are pinning all of the responsibility on one supplement, is that really true, or is it possibly another one that’s sort of tagging along, or could it just be that they are healthier to begin with?” he asked.
Social media has long abounded with claims that people need to take specific forms of folate other than folic acid based on whether they have certain gene variants. As we wrote previously, there isn’t evidence to back these recommendations. In the context of autism, Schmidt said it would be valuable to better understand how different genetic variants affect the optimal dose of folate. But she endorsed following standard recommendations on folic acid.
“That’s still the advice I would follow if I were a newly pregnant mother,” Schmidt said. “Take 400 [micrograms] folic acid supplement, on top of eating green leafy vegetables and citrus fruits and things that have folate in them.”
‘Very Weak’ Evidence on Folinic Acid in Autistic Kids
The Wall Street Journal also reported that the HHS report would highlight a form of folate, called folinic acid or leucovorin, “as a way to decrease the symptoms of autism.” Despite a variety of news coverage featuring positive anecdotes, there is very limited evidence to back the use of folinic acid in kids with autism.
“The evidence supporting folinic acid as a treatment for autism is very weak,” David S. Mandell, a psychiatry professor at the University of Pennsylvania Perelman School of Medicine and director of the Penn Center for Mental Health, told us via email. Mandell is on the executive committee of the Coalition of Autism Scientists.
The evidence consists of five small clinical trials, he said, with the number of participants ranging from 19 to 80 people. “The larger they are, the tinier the effect they find,” he said. He added that most of the studies “test many, many outcomes, without statistically adjusting for the fact that they are doing so.” The more outcomes one tests for, the more likely a positive result will occur simply by chance. Mandell also pointed out that some of the studies “use statistics that are inappropriate for a randomized trial.”
“There just really isn’t a lot of evidence in either direction,” Schmidt said, when asked about the potential of folinic acid as an autism treatment. “Just not a lot of robust, rigorous, large studies done on that topic,” she said. She added that she thought there was room for the hypothesis “to be pursued.”
In the U.S., the small clinical trial that showed an effect of folinic acid on language in children with autism was terminated for “investigator non-compliance,” according to the ClinicalTrials.gov record for the study. The sponsor of the study, the University of Arkansas for Medical Sciences, “was unable to completely monitor the study or resolve outstanding queries” and could not fully validate the data, the study record said.
High-dose folinic acid is available as a prescription drug, referred to as leucovorin, and is used as part of cancer treatment regimens. Anecdotally, some parents of autistic children are seeking folinic acid being sold as a supplement, which does not require a prescription. Supplements in the U.S., unlike drugs, do not need to be approved by the FDA as safe and effective, and there is limited oversight of supplement quality.
“There’s a long history of hawking supplements for use, and it’s not necessarily medically grounded,” Lee said.
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