In a surprising decision that could affect thousands of pending lawsuits, the Supreme Court held today that federal law preempts failure to warn claims against generic pharmaceutical companies. Justice Thomas delivered the 5-4 opinion. The Court found it was impossible for a generic company to comply with federal law requiring the generic label to be the same as the brand label, while also changing its label to include heightened warnings required by state law.

Emphasizing that “impossibility” revolved around whether a private party could “independently do under federal law what state law requires of it,” the Court analyzed the three existing avenues for effecting label changes—implementing CBE revisions, writing “Dear Doctor” letters, and petitioning the FDA for a label change. On the first two, all nine justices agreed that generic companies are prohibited from effecting unilateral label changes through either the CBE process or “Dear Doctor” letters.