The Supreme Court case brought by hundreds of Fosamax patients against Merck & Co. seems to be going the drugmaker’s way, potentially upholding the popular preemption argument the pharma industry has used to fight product liability suits.

After hearing oral arguments Monday, some of the court’s justices— including liberal Justice Stephen Breyer and conservative Justices Samuel Alito, Neil Gorsuch and Chief Justice John Roberts—appeared to support Merck’s defense, while Liberal Justices Elena Kagan and Sonia Sotomayor voiced reservations.

The dispute centers on patients’ claims that the osteoporosis drug caused "atypical femoral fractures," and that the drugmaker failed to warn them about the risk. But Merck argues that it couldn't have offered that official warning, because the FDA rejected its 2008 request to update the drug’s label. Merck says it shouldn’t be held liable under state law because it followed the federal agency's decision.

Whichever way the justices eventually land, the high court's decision would ripple through the pharma industry. The drug industry has contended that if Merck lost, biopharma companies would post speculative safety warnings. Patient advocates have argued that a ruling in favor of Merck could encourage inadequate warnings or prompt companies to deliberately give the FDA improper warnings and expect the agency's rejection to absolve them from lawsuits.

During Monday’s session, the back-and-forth boiled down to Merck’s request itself. The FDA first turned down the proposal because Merck had used the inaccurate wording of "stress fractures," which didn't reflect the more serious "atypical femoral fractures" that appeared in the label update FDA approved in October 2010, the patients argued.

But, as the administration’s Justice Department argued on behalf of Merck, the FDA was not confused by the "stress fractures" term.

"But FDA understood it to refer more generally to any fracture that was caused without external trauma," said Deputy Solicitor General Malcolm Stewart. Therefore, the agency rejected Merck’s bid not because of the language, but because it didn't have enough evidence to warrant a warning. Indeed, the FDA later initiated a task force to determine whether the drug indeed caused fractures.

Merck’s attorney argued that the FDA had seen Merck’s data and the agency has a duty to work with the drugmaker over a proper label if it feels necessary. But still, at least two Justices expressed dissatisfaction with Merck’s shifting the responsibility of investigating and coming up with a proper warning to the FDA.

"The idea that they have to look through all of your data, even though you pinpoint an entirely different risk […] and that if they don’t manage to do that, you’re exempt from suit […] it seems to conflict with the statutory provision, the rule of construction that says that manufacturers have primary responsibility over their labels," said Kagan.

Sotomayor’s remark was even more blunt: "Seems to be sort of turning responsibility on its head."

Nevertheless, other justices cautioned about publishing warnings on drugs without strong data. Such warnings might unnecessarily deter people from using an effective drug.

"The injury is that doctors are not prescribing Fosamax to women who would benefit from it and they’re not prescribing it because Merck put in a warning that the FDA would determine was over-warning," said Chief Justice Roberts in response to a remark by an attorney representing the patients.