On June 25, the Supreme Court issued a ruling with wide-ranging consequences for anyone claiming injuries related to glyphosate, the pesticide marketed as Roundup. The court’s 7-2 ruling in Monsanto Company v. Durnell effectively ends thousands of pending state-law claims that Roundup’s manufacturer failed to warn users that glyphosate could cause cancer. Conservative Justice Neil Gorsuch joined the dissent of liberal Justice Ketanji Brown Jackson.
Weed Control and Cancer: The Underlying Case
Since 1996, John L. Durnell had taken care of the weeds in the green spaces of his neighborhood in St. Louis, Missouri, as part of a beautification project. He used so much Roundup weedkiller, year after year, that people came to know him as the “spray guy.” In the 2010s, Durnell developed non-Hodgkin lymphoma, a cancer affecting the blood and lymphatic system.
By 2015, studies had emerged from the World Health Organization suggesting links between glyphosate and cancer. Durnell sued Monsanto on the grounds of product liability under Missouri law, including the company’s failure to warn properly about Roundup’s relationship to cancer. A St. Louis jury found for Durnell on that count, awarding him $1.2 million.
Monsanto — which is now part of the multinational Bayer AG — filed an appeal of Durnell’s judgment. It asserted that the company could not be liable to Durnell under Missouri law because the state of Missouri has no authority over what pesticide warning labels can say. The Environmental Protection Agency, which regulates pesticides, has so far rejected any conclusions that glyphosate can cause cancer. Thus, Monsanto did not warn about it, nor (as it argued) did it even have the option to add a warning.
The Argument: Who Has Control Over the Labeling?
According to Monsanto’s argument, federal law specifically preempts any power that a state might have to require a specific warning on a pesticide’s label. The Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) governs the sale of pesticides, including what their labels must say. One provision in FIFRA reads that a state "shall not impose or continue in effect any requirements for labeling or packaging in addition to or different from those required under this subchapter."
Monsanto argued that if Missouri law penalized the company for failing to warn Durnell about Roundup’s links to cancer, then the state effectively required a warning label “in addition to or different from” the EPA’s approved labeling. The company further contended that it did not even have the right to add such a warning without applying to the EPA, according to regulations at 40 CFR § 152.44.
The Missouri Court of Appeals disagreed. It stated that holding companies liable for a failure to warn about a product’s dangers was consistent with federal law due to FIFRA’s definition of misbranding. To avoid a misbranding violation, FIFRA requires a label to “contain a warning or caution statement which may be necessary … [and] adequate to protect health and the environment”. Thus, if Missouri were to require a cancer warning, the Court of Appeals did not consider it “in addition to or different from” the EPA’s labeling requirements.
Furthermore, the Court of Appeals said Monsanto could not claim it was totally powerless to change Roundup’s warning label. The company could have tried to do so through EPA channels by “informing the EPA of the justifications for a change,” though it does not appear that this ever happened. Thus, the opinion stated, the company could not argue that this issue created an “irreconcilable conflict between state and federal law.”
The Supreme Court’s Decision
Since there was a circuit split on the issue, the Supreme Court granted certiorari. In its June 25 opinion, the Supreme Court accepted Monsanto’s arguments, rejecting those of Durnell and courts in the Ninth and Eleventh Circuits.
Writing for the Court, Justice Brett Kavanaugh notes that Congress had added the term “Uniformity” to the law after the original Act, suggesting Congress’s emphasis on maintaining a uniform labeling scheme. He also discusses a similar Supreme Court case from 2008, Riegel v. Medtronic Inc. That case dealt with the labeling of medical devices, not pesticides, but the Supreme Court upheld the company’s arguments about a nearly identical provision of law. According to Kavanaugh, “If FDA’s premarket approval of medical devices preempted additional state-law requirements, so too must EPA’s registration of pesticides and approval of pesticide labels.”
In her dissent, Justice Jackson writes that allowing a state failure-to-warn claim for Durnell would not create a requirement “in addition to or different from” FIFRA’s labeling requirement, but instead “equivalent to” its law against misbranding a pesticide. FIFRA also provides, as she notes, that registering a pesticide and its labeling is not “a defense for the commission of any offense under this subchapter.” Jackson rejects the argument that adding a cancer warning would constitute misbranding without a formal amendment, as (according to her footnote) this has already happened several times. For his part, Justice Clarence Thomas writes a separate concurrence to assert that FIFRA is “likely unconstitutional in many applications.”
Although Bayer praised the decisions’ “regulatory clarity,” critics raised concerns that many people will be left without recourse for serious illnesses. The Trump administration supported Bayer’s position in the case and has not moved to restrict glyphosate’s federal registration, even as public‑health advocates continue to raise concerns about potential cancer risks. Those choices, combined with the Court’s ruling, could fuel political backlash among health‑conscious voters and communities already wary of pesticide exposure.
