When claims are made that one of the most widely used medications during pregnancy may cause autism, the public understandably pays attention. Scientists, healthcare professionals, and even judges, however, must ask: What does the evidence actually show?
That question is now before the U.S. Court of Appeals for the Second Circuit in New York.
The court is reviewing whether to revive more than 500 lawsuits brought by parents alleging that prenatal acetaminophen exposure caused their children’s autism or attention deficit hyperactivity disorder (ADHD).
In 2023, U.S. District Judge Denise Cote correctly excluded key expert testimony supporting those claims, concluding that they failed to meet the reliability requirements under Federal Rule of Evidence 702.
Rule 702 requires judges to ensure that expert testimony presented to juries is grounded in sufficient data, reliable methodology, and a sound application of those methods to the facts of the case. In other words, courts must act as gatekeepers to prevent speculative or methodologically unsound scientific claims from being treated as fact.
Now, plaintiffs are asking the appellate court to reverse that ruling.
The Second Circuit’s decision will test judges’ authority to prevent questionable scientific claims from reaching a jury before they satisfy established reliability standards.
This judicial gatekeeping role is essential. When expert opinions are admitted without rigorous scrutiny, litigation can amplify assumptions that have yet to meet the standards of the broader scientific community.
One reason the plaintiffs’ expert testimony was dismissed is the issue of confounding variables. Neurodevelopmental conditions such as autism and ADHD have strong genetic components. Disentangling whether a condition stems from a medication exposure or from shared familial and hereditary factors is extraordinarily complex.
None of this means the question should not continue to be studied. But when the vast majority of high-quality studies find no causation between prenatal acetaminophen use and neurodevelopmental conditions, careful gatekeeping must be exercised.
This case’s potential impact on public health makes gatekeeping even more important.
Acetaminophen is one of the most widely used medications in the world and remains the only generally recommended pain and fever reliever during pregnancy when used as directed. That guidance reflects decades of regulatory review and clinical experience.
Several studies have reported an increased likelihood of birth defects and other adverse outcomes from untreated maternal fever. Physicians routinely advise pregnant patients to treat significant fevers promptly because unmanaged fever itself can pose risks to fetal development.
If pregnant women avoid acetaminophen based on unproven claims, they may turn to alternatives such as ibuprofen or aspirin, which carry known risks later in pregnancy, including potential complications affecting fetal kidney development.
By upholding the gatekeeping responsibility of judges under Rule 702, the Second Circuit can reaffirm that scientific claims must meet established thresholds before being presented as reliable proof in court.