What the science says about Tylenol and autism

Autism is in the news in a big way thanks to the Trump administration’s recent actions. At a press conference on Sep. 22, President Donald Trump, Health and Human Services Secretary Robert F. Kennedy, Jr, and Centers for Medicare & Medicaid Services Administrator Dr. Mehmet Oz suggested that Tylenol use during pregnancy causes autism. But there’s no good science behind the administration’s conclusions about autism, and experts agree that acetaminophen, when used appropriately, safely treats fever and pain during pregnancy. (On Oct. 29, Kennedy appeared to reverse course, saying there is no 'sufficient' evidence that Tylenol causes autism.)

Why are people talking about Tylenol and autism?

A review of the scientific literature published in August 2025 claimed to find a connection between acetaminophen (the generic name for the active ingredient in Tylenol) used during pregnancy and children developing autism years later. In response, the Trump administration announced that HHS will be taking steps aimed at getting people to think twice before reaching for the drug during pregnancy by beginning the process of a safety label change for products containing acetaminophen. (Confusingly, the FDA simultaneously released a physician notice underscoring that acetaminophen is the safest painkiller for use during pregnancy.)

The recent review that’s getting so much attention was led by Dr. Andrea Baccarelli, a researcher who was once paid $150,000 to testify on behalf of parents and guardians of children with autism who were suing Johnson & Johnson, the makers of Tylenol; the case was dismissed in 2024 due to a lack of scientific evidence. When she reviewed Dr. Baccarelli’s testimony in 2023, US District Court Judge Denise L. Cote wrote that Dr. Baccarelli “cherry-picked and misrepresented study results and refused to acknowledge the role of genetics” in the development of autism.

For the review cited by the Trump administration and published in August, Dr. Baccarelli and his coauthors looked at 46 studies on the alleged connection between acetaminophen and autism spectrum disorder, attention-deficit/hyperactivity disorder, and other neurodevelopmental disorders. But just seven of those studies actually looked at autism. On top of that, methods for determining acetaminophen use were so different among the studies that the authors of the review were unable to estimate what dose of acetaminophen might increase the risk of developing autism. Consequently, they weren’t able to statistically combine the studies in a technique called meta-analysis. They just considered the studies relatively informally, using an approach that is common in assessing environmental exposures, but not medical ones.

So what does this review add to the conversation about acetaminophen and autism risk? Not that much. 

What does other research on acetaminophen and autism show?

What does the science tell us about the link between autism and acetaminophen, and why do organizations like the American College of Obstetricians and Gynecologists say acetaminophen is safe for use during pregnancy? Long story short: Although some studies have found links between acetaminophen use during pregnancy and autism in children, none of those studies show that taking the drug actually causes autism. Many other factors could explain why there might be a link.

For example, people who experience more pain and fever during pregnancy may be more likely to take acetaminophen more frequently than people with less fever and pain. But if the people who experience more pain and fever during pregnancy are also more likely to give birth to babies who develop autism, independent of their use of acetaminophen, then studies can inadvertently make it seem as though acetaminophen use is associated with autism. But that doesn’t mean that prenatal acetaminophen use causes autism.

The seven studies in the recent review can’t help us untangle the question of causation as reliably as a randomized controlled trial. That’s because in these observational studies, pregnant people or people who had recently had babies were asked at varying points about their use of acetaminophen, rather than being randomized to either receive the drug or something else for fever and pain during pregnancy. So those seven studies cannot tell us whether acetaminophen use causes autism, whether pain and fever during pregnancy (which would make pregnant people reach for acetaminophen more frequently) cause autism, or whether something else entirely could explain the increased risk.

It turns out that recent research has indeed found that fever during pregnancy is linked to babies later developing autism. For example, a 2019 study of 606 children with autism and 796 without it found that people who had an infection with a fever during the second trimester of pregnancy were more than twice as likely to have a child with autism than those who did not have a second-trimester infection. 

Some of the potential causes of autism

Scientists have identified many potential explanations, including genetic and environmental factors. For example, a 2015 review of studies of twins suggests that between 64 and 91 percent of cases of autism are caused by genetics.

And a recent study looked at nearly 2.5 million children born in Sweden between 1995 and 2019; it found a second critical clue about why studies might falsely link acetaminophen use and autism. The Swedish researchers found a 5 percent higher risk of autism in children born to a parent who took acetaminophen during pregnancy. (To be clear, even if this risk is real, it would be a minor contribution to the risk of autism overall.) But once they did what is called a sibling analysis (which focused on children born to the same biological parents), they found no evidence that acetaminophen use caused autism. Instead, they conclude that factors like genetics likely largely explain why some children develop autism and others don’t. 

Still, there could be environmental factors. A 2024 study of 318,750 children in California found that prenatal exposure to PM2.5 (particles small enough to enter the bloodstream) from sources like gasoline, diesel, and aircraft fumes was linked to the development of autism. The researchers found the highest risk for children exposed to gasoline from motor vehicles during pregnancy, who were 18 percent more likely to develop autism than children without exposure to gasoline. Too bad the Trump administration has committed to slashing environmental regulations that might protect people from vehicle emissions.  

Why autism diagnoses are on the rise

One potential reason more kids are being diagnosed with autism is that public awareness of the condition has increased. In the Public Health On Call podcast hosted by Johns Hopkins University’s Bloomberg School of Public Health, Dr. Christine Ladd-Acosta, the vice director of the Wendy Klag Center for Autism and Developmental Disabilities, explains further: “Parents, caregivers, and community members are... more aware of the symptoms, and autism is being more accepted in the community. People are not as afraid to seek help and know where to go when they have concerns.”

It’s also likely that doctors are getting better at recognizing autism in children. That’s the conclusion of a 2025 report from the CDC, which looked at autism prevalence across 16 locations in the United States. Its authors point out that California, which has a relatively high number of children with autism compared to other states, has a program through which “hundreds of local pediatricians have been trained to screen and refer children for assessment as early as possible, which could result in higher identification of [autism], especially at early ages.” The CDC report, which came out just five months before Sec. Kennedy claimed that we were seeing an autism “epidemic,” did not find any evidence for such a claim.  

On top of that, a 2015 study from Denmark concluded that changing definitions of autism that recognize it as a wide spectrum of behaviors and characteristics are responsible for 60 percent of the increase in observed prevalence of autism in that country, because a broader definition means more children will be included in it.  

Translation: There’s a good chance that much of the increase in the number of children with autism in the United States in recent years is just about how we diagnose autism, and not that more kids develop it. 

The science says appropriate prenatal use of acetaminophen is safe and effective

Although scientists are still uncovering the causes of autism, experts are in consensus about the safety of taking acetaminophen when needed during pregnancy.

A statement from the American College of Obstetricians and Gynecologists (ACOG) points out that acetaminophen is a reliable choice: “ACOG and obstetrician-gynecologists across the country have always identified acetaminophen as one of the only safe pain relievers for pregnant individuals during pregnancy.” The statement emphasizes the importance of speaking with your doctor about pain and fever during pregnancy, adding that “ACOG’s clinical guidance remains the same and physicians should not change clinical practice until definitive prospective research is done. Most importantly, patients should not be frightened away from the many benefits of acetaminophen. However, as always, any medication taken during pregnancy should be used only as needed, in moderation, and after the pregnant patient has consulted with their doctor.”

According to the Society for Maternal and Fetal Medicine (the professional organization for clinicians and researchers who specialize in high-risk pregnancy care and other related fields), untreated fevers during pregnancy have been linked to adverse outcomes, including miscarriage, birth defects, and premature birth. And untreated pain during pregnancy can cause depression, anxiety, and high blood pressure in the birthing parent. That means that pregnant people need access to—and shouldn’t be afraid to use—fever-reducing drugs like acetaminophen, both for their own safety and well-being and for the health of their babies.  

The Society’s conclusion? “Pregnant patients can be reassured that using acetaminophen to treat pain and fever is safe.” 

The bottom line

The best evidence shows no link between taking acetaminophen during pregnancy and the risk of autism in kids. Rather, acetaminophen continues to be a safe, reliable choice that pregnant people shouldn’t be made to fear.