The United States Supreme Court has sided with the maker of Roundup weedkiller in a ruling expected to block thousands of lawsuits alleging it failed to warn people the product could cause cancer.

The ruling on Thursday was tied to a case that came before the justices after a tidal wave of litigation that included some multibillion-dollar verdicts against the global agrochemical manufacturer Bayer, a Germany-based company that acquired Roundup when it bought its original producer Monsanto in 2018.

The decision is a victory for US President Donald Trump’s administration, but one that could be tricky politically since allies in the “Make America Healthy Again” movement want to rein in pesticide use.

The high court, in a 7-2 ruling, found that the company cannot face failure-to-warn lawsuits in state courts because federal regulations have found a cancer link unlikely and do not require a warning label.

The justices overturned a jury verdict in Missouri awarding $1.25m to a man named John Durnell who said he was diagnosed with non-Hodgkin lymphoma after years of exposure to glyphosate in Roundup. The Supreme Court agreed with Bayer that a US law that governs pesticides precludes failure-to-warn claims that are brought under state law from moving forward in court.

Bayer shares jumped nearly 18 percent following the ruling.

Trump’s administration had backed Bayer in the case.

Conservative Justice Brett Kavanaugh, who authored the ruling, said the US Environmental Protection Agency, or EPA, has concluded glyphosate does not cause cancer and has not required a cancer warning on Roundup.

The law preempts Durnell’s claim because it “would require Monsanto to add a cancer warning to Roundup’s label even though federal law requires Monsanto to use the EPA-approved label without a cancer warning”, Kavanaugh wrote.

Liberal Justice Ketanji Brown Jackson, in a dissent joined by conservative Justice Neil Gorsuch, said that Durnell’s claim would impose equivalent labelling requirements on Monsanto that the federal law requires and so should not be preempted.

Jackson called the ruling “remarkable and regrettable, for it unjustifiably closes the courthouse doors to state tort plaintiffs like Durnell”.

Bayer acquired Roundup as part of its $63bn purchase of agrochemical company Monsanto in 2018. More than 100,000 plaintiffs have filed cases in US state and federal courts alleging a cancer link, and the German drugmaking and crop science company had said that the lawsuits could threaten its ability to supply the herbicide to farmers.

The torrent of litigation already prompted Bayer to remove glyphosate from its consumer version of Roundup. Bayer said before the Supreme Court ruled that a decision in its favour could largely end the Roundup litigation.

“The US Supreme Court decision is good for science, farmers, and industries that depend on regulatory clarity for innovation. It should help significantly contain the Roundup litigation after nearly a decade of legal battles. The ruling should result in the dismissal of current warning-based claims and bar future failure-to-warn claims,” Bayer spokesperson Tino Andresen said in a statement.

The company emphasised throughout the litigation that the EPA repeatedly found that glyphosate does not cause cancer and approved its product labels without a warning.

Facing billions of dollars in potential liability, Bayer announced in February a proposed $7.25bn settlement to resolve tens of thousands of current and future lawsuits. The settlement would not affect claims that stem from pending appeals or that fall outside the deal, according to the company. Those amount to nearly $1bn, it said.

‘Disaster for public health’

Environmental activists and others criticised the court’s ruling on Thursday.

“Once again, the Supreme Court has sided with big business over people and the environment. Today’s ruling is a disaster for public health,” said Tarah Heinzen, legal director at the advocacy group Food and Water Watch.

“The harm from this decision will perpetuate our cancer, infertility and general chronic disease epidemic for generations to come,” said Kelly Ryerson, co-executive director of advocacy group American Regeneration and a Make America Healthy Again activist who posts on social media under the moniker “The Glyphosate Girl”.

The sprawling dispute centres on a US law called the Federal Insecticide, Fungicide and Rodenticide Act, or FIFRA, that governs the sale and labelling of pesticides and bars states from imposing differing or additional requirements.

The measure prohibits pesticides that are “misbranded” with labels that lack an adequate warning to protect health and the environment.

Bayer has argued that Durnell’s claims are preempted by this law. The EPA has repeatedly approved labels without such a cancer warning, demonstrating that these products are not misbranded, the company said, adding that labels cannot be substantially changed without the agency’s approval.

Durnell’s lawyers said that despite the EPA’s registration of Roundup, the label may still be challenged as misbranded. They also said Durnell’s claims are not preempted because Missouri state law that requires products to adequately warn of dangers imposes the same requirements as FIFRA’s prohibition on misbranding.

‘A new era’

Union Investment fund manager Markus Manns called Thursday’s ruling a significant milestone for Bayer, adding that a decade after the Monsanto acquisition, the company is “entering a new era”.

“While future lawsuits are not entirely off the table, they will become considerably more difficult. A final breakthrough would come if the settlement is accepted by the plaintiffs and approved by the competent court in July. This would bring Bayer’s glyphosate litigation chapter to a definitive close, allowing management to fully refocus on operational and strategic matters,” Manns said.

Durnell sued Monsanto in Missouri state court in 2019, claiming it failed to warn users of the dangers associated with Roundup and glyphosate.

He was diagnosed with a rare and often aggressive form of non-Hodgkin lymphoma, a cancer that starts in the white blood cells, and attributed the disease to his exposure to Roundup starting in 1996. For about 20 years, he was the “spray guy” for a neighborhood association in St Louis, killing weeds at local parks without protective equipment, according to court papers.

A jury sided with Durnell in 2023, and in 2025, a state appeals court upheld that verdict.