Supreme Court Weighs in on Missouri Failure to Warn Claim: Finds Preempted by Federal Statute
Glyphosate is a broad-spectrum systemic herbicide used to block enzyme pathways plants need to synthesize proteins, which causes them to slowly die. It is used in hundreds of products, but most famously, Roundup. Manufactured by Monsanto and Bayer, Roundup has been the subject of tens of thousands of lawsuits, based on the allegation that the herbicide not only kills plants, but also potentially causes non-Hodgkin’s lymphoma and other blood cancers, while failing to adequately warn consumers about the risks associated with it.
However, Roundup is not the only pesticide on the market. The use of such pesticides, herbicides, and other solutions became so prevalent that Congress passed the Federal Insecticide, Fungicide, and Rodenticide Act (“FIFRA”), 7 U.S.C. § 136 – 136y. In that act, Congress authorized the EPA to regulate the distribution, sale, production, and use of pesticides and pesticide devices in the United States. All (with certain exceptions) pesticides must be registered by the EPA before they can be distributed or sold in the United States, and as part of this registration, the applicant must show that the use of the pesticide “will not generally cause unreasonable adverse effects on the environment.” Under FIFRA, the EPA specifically addresses what is and is not included on the labels. Finally, FIFRA requires uniformity in labeling, preempting and prohibiting states from imposing additional pesticide requirements in addition to or different from the federal requirements under FIFRA.
Roundup is included under the regulations imposed by FIFRA. As part of its regulatory analysis, the EPA has repeatedly concluded that glyphosate is not likely to cause cancer. As a result, the EPA has not required a cancer warning label on Roundup.
In 2019, John Durnell brought suit against Monsanto in the Circuit Court of the City of St. Louis, alleging that he developed non-Hodgkin’s lymphoma from the use of Roundup. Mr. Durnell brought claims for strict liability in the defective design and failure to warn, and negligence. After a jury trial, Monsanto moved for a directed verdict on the grounds that Mr. Durnell’s claims were barred by FIFRA. The Trial Court denied the motions, and the jury returned a verdict in favor of Mr. Durnell. Monsanto appealed, and the Missouri Court of Appeals sitting in the Eastern District affirmed the judgment of the trial court, finding that federal preemption under FIFRA did not apply, because Missouri’s common law failure to warn action does not impose a requirement “in addition to or different from” the requirements of FIFRA. See Durnell v. Monsanto Company, 707 S.W.3d 828 (Mo. App. E.D. 2025). After the Missouri Supreme Court denied Monsanto’s application for transfer, Monsanto filed a petition of writ of certiorari to the United States Supreme Court, which granted certiorari on the issue. Justice Kavanaugh wrote the majority opinion of the Court. See Monsanto Company v. Durnell, 609 U.S. — (2026).
Focusing specifically on FIFRA’s “uniformity” requirements under 7 U.S.C. § 136v(b), the majority found that permitting states to impose additional requirements in labeling (for example, to include cancer warnings on Roundup) would render FIFRA’s preemption clause “impossible to achieve.” 609 U.S. at *6. Ultimately, the Court relied upon the fact that once the EPA approves a label at registration, manufacturers are required to use that label. Id. at *7. Failure to do so imposes civil and criminal penalties on it. As a result, the common law failure-to-warn claim against Monsanto for failing to include cancer warnings would require Monsanto to include a label that is specifically not approved by the EPA. This places Monsanto in a double-bind situation; including the warning violates FIFRA, whereas not including the warning would, as the Missouri Court of Appeals found, violate Missouri’s common law failure-to-warn requirements. Accordingly, the Majority found the Missouri law constituted a requirement “in addition to” and “different from” Monsanto’s federal-law labeling obligations, thereby rendering the failure-to-warn claims preempted under FIFRA. Id. at *8.
The dissent, authored by Justice Jackson and joined by Justice Gorsuch, argued that FIFRA’s regulated warnings do not have a preempting effect; but rather, FIFRA and the common law failure to warn claim can operate in parallel, providing “a traditional damages remedy for violations of common-law duties…” Id. at *16 (J. Jackson, dissenting).
Ultimately, the Court reversed the judgment of the Missouri Court of Appeals and remanded the case for further proceedings consistent with their opinion. Id. at *13.
Monsanto v. Durnell has significant precedential effect on cases involving pesticides. However, Monsanto also has deeper implications for federal preemption of state law claims where administrative agencies impose particularized requirements upon manufacturers. If those requirements are express, failure to warn claims may be barred in full. It is therefore important to understand both federal and state regulations, and understand which prevails in a conflict.
You can read the full opinion here at: https://www.supremecourt.gov/opinions/25pdf/24-1068_n7ip.pdf