Afiqah Yusuf, PhD, is a health scientist specializing in evidence synthesis and global health, with deep expertise in autism research. She has led systematic reviews, randomized trials, and capacity-building initiatives on autism in partnership with global organizations and major research networks. At Precision Analytics, she focuses on bringing scientific rigor to high-stakes debates, ensuring that data, methods, and conclusions meet both scientific and legal standards.

On September 22, 2025, the White House staged a press conference with Robert F. Kennedy Jr. and senior health officials, claiming that Tylenol use in pregnancy causes autism [1]. Scientists swiftly pushed back. Acetaminophen remains one of the safest painkillers for expectant mothers, and the few studies cited at the event were methodologically weak. Medical and scientific groups spent the week reassuring the public that acetaminophen is safe during pregnancy [2].

The supposed link between acetaminophen and autism is not new. It had already been tested in US federal court and rejected since 2023 for lack of reliable evidence [3]. Its sudden return—just as appeals are underway in an attempt to revive the case [4] —looks less like science and more like strategy.

Understanding the litigation surrounding the acetaminophen claims is essential, because it may be the real driver of this recent wave of media coverage. As the Wall Street Journal reported, law firms suing the makers of Tylenol have a clear strategy:

“The transparent goal is to drum up more claims to drive a bigger damage award or settlement…conveniently timed for their appeal at the Second Circuit Court of Appeals this fall” [5].

And it looks like the strategy is working: one plaintiff’s firm has reportedly been receiving “more than a thousand calls” from potential clients in a week [6].

In other words, the recent publicity may not be about protecting families or serving the autistic community, nor is it about “new evidence.”

In 2022, claims against the makers of acetaminophen were filed in the United States District Court for the Southern District of New York, alleging that prenatal acetaminophen exposure caused autism [7]. To support these claims, the plaintiffs put forward expert witnesses who tried to argue a scientific link.

One of the lead experts was Dr. Andrea Baccarelli, whose work was featured prominently in the recent media coverage fueling the acetaminophen–autism claims. But, Judge Denise Cote, after reviewing his expert report and deposition, ruled that Dr. Baccarelli’s testimony was unreliable and excluded it from trial [8].

Because the other experts’ reports relied heavily on his analysis, their testimony fell with his. Without that foundation, the case was thrown out. The dismissal matters beyond the courtroom, as the same arguments have resurfaced in recent discussions—raising questions about their renewed prominence at this particular moment.

The decision rested on the Daubert standard, which comes from a 1993 Supreme Court ruling that requires judges to act as “gatekeepers” for expert testimony. Under Daubert and Rule 702 of the Federal Rules of Evidence, expert opinions are admissible only if they are relevant, based on sufficient data, and use reliable methods applied correctly [9]. These rules are designed to prevent juries from being swayed by testimony that mistakes correlation for causation or relies on weak methods. Judges evaluate whether an expert’s approach is testable, peer-reviewed, reproducible, and generally accepted in the scientific community.

Judge Cote found that the plaintiffs’ experts did not meet this bar in claiming that acetaminophen causes autism [8].

Judge Cote zeroed in on the testimony of Dr. Baccarelli, concluding that his methods fell short of the standards the law requires for expert evidence [8]:

• Mixing diagnoses: Dr. Baccarelli lumped autism, ADHD, and other neurodevelopmental disorders into one big “transdiagnostic” category. That may make the data look stronger, but it blurs important distinctions. Judge Cote noted that this inflated the number of studies cited while obscuring whether acetaminophen was linked to autism specifically.

• Cherry-picking studies: Dr. Baccarelli dismissed certain research for methodological weaknesses while relying on other studies with the very same flaws. For example, he downplayed one study because its outcomes were measured using parent questionnaires—yet cited another study using the same methods as supportive evidence without raising the same concern.

• Inconsistent evidence: In the trial, Judge Cote noted that out of the six studies on acetaminophen and autism: three showed no link, one suggested a protective effect, one found a link only when ADHD was also present, and just one suggested a positive association (although with serious flaws that we will detail in an upcoming article). Rather than admitting that the body of literature is heterogeneous, Dr. Baccarelli insisted on its consistency, which Judge Cote noted as “misleading”, adding:

“It is difficult to understand where Dr. Baccarelli was looking when he found that the research regarding ASD was consistent…”

• Ignoring confounding factors: Confounding factors are variables that influence both the supposed “cause” and “effect,” making it look like one causes the other. In this case, conditions such as fever or genetic predispositions may both increase the risk of autism and increase the likelihood of acetaminophen use during pregnancy—creating a misleading association. Dr. Baccarelli didn’t properly account for genetics and fever/pain—key issues in a causal analysis between acetaminophen and autism. Judge Cote wrote in her judgement:

“By itself, this failure requires the exclusion of his opinion.”

To make their case, the plaintiffs’ experts leaned on the Bradford Hill criteria - a set of nine guidelines scientists use to determine whether an association might actually be causal [10]. To explain how these criteria apply, we invited Precision Analytic’s Scientific Advisor, Dr. Robert Platt , Professor of Epidemiology and Biostatistics at McGill University, and a perinatal epidemiologist internationally recognized for his work on maternal and child health. Dr. Platt has authored more than 400 scientific publications and leads large-scale studies on medication safety in pregnancy, pharmacoepidemiology, and causal inference. He has also served as an expert witness in cases where the reliability of scientific evidence was under scrutiny, giving him a unique perspective on how courts evaluate complex epidemiological data.

As Dr. Platt explains:

The Bradford Hill criteria, or viewpoints, are a framework for thinking about causation, not a mechanical test. Their purpose is to help interpret the totality of evidence, including biological plausibility, coherence with existing knowledge, and consistency across studies— not to replace statistical rigor or to act as a stand-alone tool for causal inference. When applied carefully, they help distinguish between associations that are meaningful and those that are the result of bias, chance, or confounding. However, Dr. Hill himself emphasized flexibility and context, noting that none of the criteria are individually necessary nor collectively sufficient for establishing causation

Judge Cote found that the plaintiffs’ experts failed to meet this standard. Dr. Baccarelli’s analysis along with that of other experts brought on by the plaintiffs was deemed “cursory” and failed to grapple with the “remarkable degree” of inconsistency across studies [8]. Most importantly, they overlooked evidence of genetic confounding. Her conclusion was blunt: Dr. Baccarelli “obscured instead of informed” the inquiry into causation [8].

Outside the courtroom, the science points in the same direction: there’s no reliable evidence that acetaminophen in pregnancy causes autism. Since the trial, Dr. Baccarelli has published a review of the scientific literature, purporting that studies showed a link between acetaminophen and neurodevelopmental disorders, including autism and ADHD [11]. However, he makes the same errors here as the trial, inflating the number of studies under an umbrella of “neurodevelopmental disorders” [11]. When limiting to autism, the number of studies that found an association went down to four (versus four that showed null associations) [11]. While no study is perfect, this handful of studies continue to have the limitations noted by Judge Cote in 2023, especially in regards to addressing the issue of confounding factors.

We delve into the specific limitations of each of these studies, along with the problem in Dr. Baccarelli’s review in our next articles in the series, but briefly, one major confounding factor is why expectant mothers take acetaminophen in the first place.

We spoke directly with Dr. Eric Fombonne , Professor Emeritus of Psychiatry at Oregon Health Science University, a child psychiatrist, autism researcher, and epidemiologist with decades of experience leading large population studies on autism. Dr. Fombonne has authored more than 400 scientific publications, including seminal work on the prevalence, causes, and outcomes of autism, and has served as an expert witness in multiple cases involving the evaluation of autism research. He explained:

“Since the reasons for taking acetaminophen—migraine, fever, pain—are not always recorded or recalled accurately, confounding by indication is pervasive in those studies.”

Dr. Fombonne also emphasized the role of genetics. The same genetic factors that increase the likelihood of autism may also increase the likelihood of conditions—such as migraines, fever, or pain—that lead to acetaminophen use during pregnancy. When researchers properly account for these genetic influences, the apparent link disappears:

“Any associations found between acetaminophen and autism disappeared in sibling analyses, providing strong evidence against a causal link between prenatal acetaminophen exposure and risk of autism.”

Judge Cote raised the same concerns in excluding the plaintiffs’ experts: they ignored confounding and relied on selective readings of inconsistent evidence. In both science and law, the claim does not withstand scrutiny.

What is clear, however, is that untreated fever in pregnancy poses real risks for both mother and baby—including complications such as preterm labor and ironically, neurodevelopmental conditions [12, 13]. That is why acetaminophen remains one of the safest and most effective options for managing fever during pregnancy. As Dr. Platt explains:

“One of the most important things to remember is that untreated fever itself poses risks for both mother and baby, and that other medications like NSAIDS (e.g., ibuprofen) may also pose risks. We have decades of evidence showing that high maternal temperature can contribute to preterm labor, miscarriage, and even neurodevelopmental problems in the child.”

Much of the recent attention stems not from new scientific findings. The timing of this news—coinciding with an appeal against the makers of Tylenol—raises questions about whether it is truly motivated by protecting families.

As Dr. Mayada Elsabbagh , Professor, Department of Neurology and Neurosurgery at McGill University, cautioned:

“The real story is that science is being weaponized. Genuine scientific integrity requires both defending truth and exposing power.”

Families, however, deserve confidence, not confusion. The science is clear: acetaminophen use in pregnancy does not cause autism. Courts have now reinforced that message by demanding rigorous, reliable methods from expert witnesses—and excluding those who fell short. For lawyers and scientists alike, the case is a reminder that careful, transparent analysis is the only way evidence can stand up—whether in journals or in court.

• The application of the Bradford Hill criteria in litigation
• A critical review of the limitations of studies driving the acetaminophen–autism claims
• The methodological problems underlying poor systematic reviews

1. The White House. (2025, September 22). FACT: Evidence Suggests Link Between Acetaminophen, Autism. The White House. https://www.whitehouse.gov/articles/2025/09/fact-evidence-suggests-link-between-acetaminophen-autism/

2. Pearson, H., & Ledford, H. (2025). Trump links autism and Tylenol: is there any truth to it? Nature, 646(8083), 13–14. https://doi.org/10.1038/d41586-025-02876-1

3. In re Acetaminophen-ASD-ADHD Prods. Liab. Litig., No. 1:22-md-03043-DLC, ECF No. 1421 (S.D.N.Y. Jan. 15, 2024) (Final Judgment), https://www.courtlistener.com/docket/65408277/in-re-acetaminophen-asd-adhd-products-liability-litigation/?page=9

4. In re Acetaminophen-ASD-ADHD Prods. Liab. Litig., No. 1:22-md-03043-DLC, ECF No. 1601 (S.D.N.Y. Jul. 21, 2025) (Notice of Appeal), https://www.courtlistener.com/docket/65408277/in-re-acetaminophen-asd-adhd-products-liability-litigation/?page=11

5. Trump, Tylenol and the Plaintiffs Bar. (2025, September, 23). The Wall Street Journal. https://www.wsj.com/opinion/tylenol-acetaminophen-autism-donald-trump-rfk-jr-fda-pregnant-women-548bb877

6. Lupkin, S. (2025, September, 29). Lawsuits against Tylenol’s maker get a boost after Trump’s comments. National Public Radio. http://npr.org/sections/shots-health-news/2025/09/29/nx-s1-5554865/tylenol-autism-lawsuit-kenvue-trump

7. In re Acetaminophen-ASD-ADHD Prods. Liab. Litig., No. 1:22-md-03043-DLC, ECF No. 1 (S.D.N.Y. Oct. 1, 2022) (Conditional MDL Transfer), https://www.courtlistener.com/docket/65408277/in-re-acetaminophen-asd-adhd-products-liability-litigation/?page=1

8. In re Acetaminophen-ASD-ADHD Prods. Liab. Litig., No. 1:22-md-03043-DLC, ECF No. 1381, (S.D.N.Y. Dec. 18, 2023) (Order re: Mot. to Exclude Pls. Experts), https://www.courtlistener.com/docket/65408277/in-re-acetaminophen-asd-adhd-products-liability-litigation/?page=9

9. Rule 702. testimony by expert witnesses. (n.d.) Legal Information Institute Cornell Law School. https://www.law.cornell.edu/rules/fre/rule_702

10. Fedak, K. M., Bernal, A., Capshaw, Z. A., & Gross, S. (2015). Applying the Bradford Hill criteria in the 21st century: how data integration has changed causal inference in molecular epidemiology. Emerging Themes in Epidemiology, 12(1), 14. https://doi.org/10.1186/s12982-015-0037-4

11. Prada, D., Ritz, B., Bauer, A. Z., & Baccarelli, A. A. (2025). Evaluation of the evidence on acetaminophen use and neurodevelopmental disorders using the Navigation Guide methodology. Environmental Health, 24(1), 56. https://doi.org/10.1186/s12940-025-01208-0

12. Antoun, S., Ellul, P., Peyre, H., Rosenzwajg, M., Gressens, P., Klatzmann, D., & Delorme, R. (2021). Fever during pregnancy as a risk factor for neurodevelopmental disorders: results from a systematic review and meta-analysis. Molecular Autism, 12(1), 60. https://doi.org/10.1186/s13229-021-00464-4

13. Dreier, J. W., Andersen, A.-M. N., & Berg-Beckhoff, G. (2014). Systematic Review and Meta-analyses: Fever in Pregnancy and Health Impacts in the Offspring. Pediatrics, 133(3), e674–e688. https://doi.org/10.1542/peds.2013-3205