Texas Attorney General Ken Paxton, R, sued the makers of Tylenol this week, stating that the companies ignored and silenced emerging evidence linking acetaminophen, the active ingredient in Tylenol, with an increased risk of autism and other neurological disorders. Johnson & Johnson, which manufactured Tylenol for decades, and Kenvue, a now-independent company that split from J&J in 2023, are both named as defendants in the lawsuit.
The lawsuit follows President Donald Trump’s remarks in late September in which he warned pregnant women about taking Tylenol.
“I want to say it like it is. Don’t take Tylenol. Don’t take it. If you just can’t, I mean, fight like hell not to take it. There may be a point where you have to, and you have to work it out with yourself,” Trump told reporters in the Oval Office flanked by Department of Health and Human Services head Robert F. Kennedy, Jr., and Mehmet Oz, administrator for the Centers for Medicare and Medicaid Services.
Numerous health organizations, including the American College of Obstetricians and Gynecologists, the American Academy of Pediatrics, Autism Science Foundation and the World Health Organization, quickly pushed back against Trump’s remarks and emphasized that there is no conclusive scientific evidence linking Tylenol use during pregnancy to autism.
“Any association between acetaminophen and autism is based on limited, conflicting and inconsistent science and is premature,” Autism Science Foundation Chief Science Officer Dr. Alycia Halladay said in a press release.
Back in 2021, a group of 91 scientists, clinicians and public health professionals published a consensus statement about acetaminophen use during pregnancy, noting its potential to interfere with fetal development and increase risks of some neurodevelopmental, reproductive and urogenital disorders.
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Mounting legal action against Tylenol makers
Texas is the first state to file a lawsuit against the makers of Tylenol, but parents and concerned citizens have filed hundreds of lawsuits in recent years.
In 2022, around 90 lawsuits filed in federal courts were consolidated into a multidistrict litigation, or MDL, in which a single judge presides over all the cases to streamline the process and ensure consistency. Judge Denise Cote in the Southern District of New York ultimately dismissed the cases in August 2024, ruling that there was insufficient medical and scientific evidence supporting the link between Tylenol and autism.
The plaintiffs’ lawyers have appealed, and court proceedings are expected to begin again next month, according to Matt Dolman, one of the lawyers leading the case.
There are several other ongoing lawsuits at the state level.
Warning labels
The same day as Trump’s September press conference, the Food and Drug Administration moved to change warning labels on products containing acetaminophen.
“The FDA is taking action to make parents and doctors aware of a considerable body of evidence about potential risks associated with acetaminophen,” FDA Commissioner Marty Makary said at the time.
“Even with this body of evidence, the choice still belongs with parents. The precautionary principle may lead many to avoid using acetaminophen during pregnancy, especially since most low-grade fevers don’t require treatment. It remains reasonable, however, for pregnant women to use acetaminophen in certain scenarios.”
The FDA also released a letter to physicians, instructing them to consider limiting acetaminophen use for pregnant women with low-grade fevers.
Tylenol is not the only medication that contains acetaminophen. This active ingredient is found in many common pain relievers and cold and flu remedies, including Alka-Seltzer Plus, Pamprin and certain types of Benadryl, Robitussin, Sudafed and Theraflu products.
Acetaminophen is the only over-the-counter drug approved to treat fever during pregnancy, which itself has been linked to heightened risks of autism for the developing child.
One study that followed over 95,000 children in Norway found that a fever during the second trimester increased the risk of autism in the child by 40% while three or more fevers after the first trimester increased the risk by over 300%.
What do we know about links between autism and acetaminophen?
In August, researchers published a meta-analysis that brought together many previous studies examining the use of acetaminophen and the risk of neurodevelopmental disorders. The scientists pooled the data and statistics from those independent papers and then analyzed that larger dataset for any consensus findings.
In total, the scientists reviewed 46 studies. Of those, 27 studies reported that acetaminophen use during pregnancy was related to an increased risk of a child developing autism and ADHD. Nine studies found no association, while four found that acetaminophen may prevent neurodevelopmental disorders.
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According to the CDC, 1 in 31 eight-year-olds in the U.S. was diagnosed with an autism spectrum disorder this year.
Many studies also found a dose-response relationship, meaning that higher levels of acetaminophen consumption were associated with a higher risk of a child developing autism or ADHD.
These studies do not prove that acetaminophen causes autism or other neurodevelopmental disorders. Since fever itself is linked to a higher risk of autism, and pregnant women can take acetaminophen to treat fever, Tylenol usage could simply act as a signal for the fever, not causing the risk by itself. In other words, acetaminophen use could show up in the data because it is tied to an underlying health issue, not because the drug is directly impacting the baby.
Studies like these that assess links between acetaminophen use and autism are observational studies, and they have limitations. In such studies, scientists follow a group of pregnant women — and, in this case, their children. The scientists collect data on certain behaviors and outcomes — such as an autism diagnosis — and look for patterns that link behaviors or risk factors with those outcomes.
The strength of evidence from observational studies is weaker than that from experimental studies, which allow researchers to closely control a single factor of interest and thus better understand its impact on a specific outcome.
However, scientists cannot perform controlled experiments among pregnant women due to ethical concerns and codes. As a result, observational studies, supplemented at times by animal experiments, are often the most reliable evidence available.
But there are many factors that might play a role in autism risk, including genetics. Autism is known to be hereditary, meaning it can be passed from parents to children. One meta-analysis estimated that 60% to 90% of autism risk is genetic.
A large study that followed almost 2.5 million children in Sweden aimed to understand the correlation between acetaminophen use during a mother’s pregnancy and risk of a child being diagnosed with autism, ADHD or an intellectual disability. However, these researchers took their analysis one step further and conducted a sibling analysis to understand the role genetics played in this phenomenon.
The researchers compared siblings from the same family, where one sibling was exposed to acetaminophen and the other was not. The nearly 2.5 million children followed in the study included approximately 1.7 million siblings representing about 780,000 families. The sibling analysis found that exposure to acetaminophen in utero was not significantly associated with risk, suggesting that genetics played a role in driving the association.
