In a significant win for a St.Louis-based chemical manufacturer, the U.S. Supreme Court on Thursday overturned a judgment in favor of a Missouri man who contended that the manufacturer's Roundup weedkiller caused his cancer.
In a 7-2 decision, the court ruled that Monsanto was not obligated to warn customers of a potential cancer risk because the Environmental Protection Agency has not required such labelling on the popular product. For years, the EPA has held that glyphosate, the most common herbicide used in U.S. agriculture and a key ingredient of Roundup, is noncarcinogenic, though a key international agency has contradicted that view.
The court ruled that Monsanto was not required to label because the provisions in the federal statute say plainly that states, Missouri in this case, “…shall not impose or continue in effect any requirements for labeling or packaging in addition to or different from those required under” the statute.
In a lengthy dissent, Justice Ketanji Brown Jackson argued that the court majority “reads into FIFRA a labeling requirement that does not exist, and it reads out of FIFRA the statute’s ongoing prohibition on misbranding.”
Jackson, who was joined in her dissent by Justice Neil Gorsuch, concluded: “Ultimately, the effect of the majority’s interpretation is both remarkable and regrettable, for it unjustifiably closes the courthouse doors to state tort plaintiffs like Durnell.”
Though the court's decision focused narrowly on labelling requirements and not the question of whether Roundup ingredients cause cancer, it could have significant implications for thousands of lawsuits brought against Monsanto by Americans who claim they were sickened by Roundup.
The German pharmaceutical and life sciences giant Bayer, which now owns Monsanto, set aside $16 billion to settle a tsunami of lawsuits over the weedkiller when it purchased the company.
In 2025, a Missouri jury decided that Monsanto failed to warn St. Louis resident John Durnell about the possible carcinogenic properties Roundup, as required by Missouri law. Durnell claims that he developed non-Hodgkins lymphoma as a result of using Roundup, which contains the controversial chemical glyphosate.
The Missouri jury awarded Durnell $1.25 million in damages.
The Missouri Court of Appeals upheld the jury award, which prompted Monsanto to appeal to the U.S. Supreme Court.
Monsanto argued that it was not required to label the product because such labeling was not required by the EPA.
The court's majority, an unusual combination of liberal and conservative justices, ruled in favor of Monsanto's contention that EPA’s past approval of glyphosate preempts Missouri’s failure-to-warn laws.
Since 1947, the Federal Insecticide, Fungicide, and Rodenticide Act, has acted as the federal statute that governs the labeling and sale of pesticides in the U.S.
In 2015, the International Agency for Research on Cancer, a part of the World Health Organization, broke from years of glyphosate-related decisions and classified the chemical as “probably carcinogenic to humans.” In response, the EPA said that it “considered a significantly more extensive and relevant dataset” than the IARC, and it does not agree with the agency’s conclusion.
This classification launched over 100,000 cases against chemical manufacturers, with many centering around Monsanto.
In briefs submitted to the court before oral arguments, both sides claimed that FIFRA proves their case.
Monsanto points to a part of the act that states, “EPA prohibits the sale and distribution of unregistered, adulterated, or misbranded pesticides and the use of any registered pesticide in a manner inconsistent with its labeling.”
“(Durnell’s) label-based failure-to-warn claim is preempted twice over,” said Paul Clement, the lawyer representing Monsanto, during oral arguments before the Supreme Court.
“Here, a Missouri jury imposed a cancer warning requirement that the EPA does not require,” Clement said. “That additional requirement is preempted.”
The company states that because the EPA has always approved its labels and the use of glyphosate in its products, FIFRA preempts Missouri’s state failure-to-warn laws. It points to FIFRA’s strict uniformity clauses, and claims that if every state has their own say, it would create an unnecessary burden on the company to create 50 different labels for the same product.
It also uses FIFRA to affirm that it would not have been able to add an unsanctioned cancer warning to its product. In the Missouri trial, Durnell’s lawyers said there was no evidence that Monsanto had ever submitted a possible cancer warning to the EPA.
Durnell's lawyers pointed to another part of the act that states, “Under FIFRA, States have broad authority to regulate pesticides…”
“Missouri thus requires adding cancer warnings, but federal law requires EPA to approve new warnings and tasks EPA with deciding what label changes would mitigate any health risks,” said Ashley Keller, the lawyer representing Durnell, during oral arguments.
“State law must give way,” Keller added.
This specific quote from the act does go on to say, “...however, it is unlawful for States to impose or continue in effect any requirements for labeling or packaging in addition to or different from those required under FIFRA.”
In a statement released immediately after the ruling, the company seemed to be pleased with how the opinion would affect the ongoing cancer litigation.
"(The decision) should help significantly contain the Roundup litigation after nearly a decade of legal battles," said the company in their statement. "The ruling should result in the dismissal of current warning-based claims and bar future failure-to-warn claims."
The company added that it "...will continue to pursue final approval of the class settlement and other elements of its multi-pronged strategy to contain the Roundup litigation."
