A federal appeals court is considering whether to reinstate more than 500 lawsuits brought by parents who allege that prenatal exposure to Tylenol caused their children to develop autism or attention deficit hyperactivity disorder (ADHD).

The cases were thrown out in December 2023 by U.S. District Judge Denise Cote, who ruled that the plaintiffs’ scientific experts failed to present reliable evidence linking acetaminophen use during pregnancy to the conditions. Cote criticized the expert analyses as “unstructured,” saying they relied on cherry-picked data and overlooked major inconsistencies in the research.

But during a hearing this week, two judges on the U.S. Court of Appeals for the Second Circuit suggested that at least some expert testimony may have been wrongly excluded — and that the lawsuits might have been dismissed too early.

“I’m having trouble understanding why the district court was correct to say that this just is nonsense,” Judge Gerard Lynch said. “It seems to me that you have a reputable scientist explaining why each of these judgment calls was made.”

Judge Guido Calabresi also questioned whether the cases should have been allowed to proceed to trial.

“It seems to me you’re constantly coming back to where you began, which is [the experts] didn’t show that there was a causal link,” Calabresi said. “But a causal link cannot be shown. All that matters is if people bring in evidence so that juries or courts may say, ‘This goes one way or the other.’”

The panel did not indicate when it would issue a ruling on whether the lawsuits can move forward.