The majority of evidence that shows an association between taking Tylenol (acetaminophen) during pregnancy and autism or Autism Spectrum Disorders (ASD) has been from observational studies, and some medical experts are questioning the legitimacy of those studies. 

Dr. Tabitha Quebedeaux, M.D., Ph.D., who specializes in obstetrics, gynecology, and maternal-fetal medicine, and holds her doctorate in neuroscience, told a New Orleans news station that observational studies do not take into account other risk factors that may have led to a child’s autism. 

“So, the studies that they're referencing, don't control for that, and so you really can not say that there's a causal link of taking Tylenol and causing autism in our kids,” Dr. Quebedeaux told WWL, which also interviewed epidemiologist Dr. Emily Harville of Tulane University, who suggested that observational studies are not as strong as controlled ones. For instance, people may be unable to recall their past intake of acetaminophen because it’s not prescribed by a doctor. 

Observational studies are separate from controlled studies in that they do not seek to control for variables but instead simply note correlations within sets of data. Observational studies are an excellent jumping-off point for designing controlled trials, but they should not be considered definitive proof of a phenomenon.

In October 2022, over 80 acetaminophen-autism lawsuits filed in federal courts were consolidated in multidistrict litigation (MDL), assigned to the Southern District of New York under Judge Denise Cote. As of March 10, there were 107 cases pending in the MDL. Considering the popularity of Tylenol—an estimated 65% of pregnant women use Tylenol—and the rate of autism or ASD is approximately 1 in 36 children, plaintiffs' attorneys expect tens of thousands of new cases to be filed. 

Defendants in the MDL include retail pharmacy giants including Walmart, CVS, and Walgreens. Walmart filed a motion to dismiss the lawsuits, but Judge Cote denied the motion in March. Plaintiffs accuse the drug giants of failing to warn them about the link between autism and acetaminophen, which is an active ingredient in several other brands of over-the-counter medicines, including Nyquil, Dayquil, Robitussin, and Alka-Seltzer.
Plaintiffs' attorneys began filing the lawsuits mostly after a 2018 observational study published in the American Journal of Epidemiology concluded that “Acetaminophen use during pregnancy is associated with an increased risk for ADHD, [Autism Spectrum Disorder], and hyperactivity symptoms.” 

In 2021, 91 medical experts published a consensus statement in Nature Reviews Endocrinology, recommending that pregnant women should be cautioned at the beginning of pregnancy to:

  • Forego acetaminophen unless its use is medically indicated
  • Consult with a physician or pharmacist if they are uncertain whether use is indicated and before using on a long-term basis
  • Minimize exposure by using the lowest effective dose for the shortest possible time 

“This Consensus Statement reflects our concerns and is currently supported by 91 scientists, clinicians, and public health professionals from across the globe,” the experts concluded.

In October, Judge Cote is expected to rule on whether the scientific causation is valid. 

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