The United States Supreme Court ruled on Thursday that federal law shields Bayer from lawsuits alleging it failed to warn consumers that its Roundup weedkiller could cause cancer, a decision that immediately blocks tens of thousands of claims and sent the German company’s shares up by more than 15%. The 7-2 majority held that the Federal Insecticide, Fungicide, and Rodenticide Act preempts state-level requirements for additional health warnings, because the Environmental Protection Agency (EPA) has consistently determined that glyphosate, the herbicide’s active ingredient, is unlikely to be carcinogenic to humans when used as directed and has approved a label without a cancer warning.

The ruling resolves a central legal question that had fuelled mass litigation since Bayer acquired Roundup’s original manufacturer, Monsanto, in 2018. Bayer argued that it could not be held liable under state law for omitting a warning that federal regulators had deliberately declined to require. The Supreme Court agreed, with Justice Brett Kavanaugh writing that EPA’s approval of the label meant any additional state-mandated warning would constitute an impermissible “requirement additional or different” from the federal standard. In a dissenting opinion, Justices Neil Gorsuch and Ketanji Brown Jackson called the decision “remarkable and regrettable,” saying it “unjustifiably closes the courthouse doors” to plaintiffs. The World Health Organization’s International Agency for Research on Cancer (IARC) classified glyphosate as “probably carcinogenic” in 2015, a finding that has been central to the litigation but which the EPA and other national regulators, including in the European Union, have not adopted.

Viewed from Washington, the decision reinforces the primacy of federal regulatory science over state tort law, a principle with implications beyond the agrochemical sector. The Trump administration had sided with Bayer in the case, a stance that has opened a rift with the “Make America Healthy Again” (MAHA) movement, whose supporters helped elect the president and have long demanded tighter restrictions on pesticides. Health Secretary Robert F. Kennedy Jr. has repeatedly stated that glyphosate causes cancer, even as he acknowledged the administration’s executive order to boost domestic production of the chemical for food-supply and national-security reasons. MAHA activists have publicly expressed frustration, and some are now backing primary challengers to Trump-endorsed candidates, signalling a potential realignment of the coalition ahead of the 2028 election.

Bayer has already paid more than $10 billion in settlements and verdicts related to Roundup, and the company had set aside an additional $16 billion to resolve remaining claims. In February it proposed a $7.25 billion class-action settlement to address current and future litigation; that settlement is pending before a Missouri state court and would establish a compensation fund for cancer patients, with payouts likely lower than those awarded at trial. The Supreme Court ruling does not affect claims based on alleged design defects, but it removes the legal basis for the majority of the roughly 67,000 unresolved failure-to-warn cases. Bayer’s chief executive, Bill Anderson, said the decision “brings long-overdue justice and clarity” and would help the company contain the litigation by the end of 2026. The EPA’s position remains unchanged, and the company has stated it will continue to defend the safety of glyphosate in the remaining proceedings.