Supreme Court heard arguments in Bayer's Roundup cancer case that could gut 100,000 lawsuits

The justices are weighing whether federal pesticide law blocks state failure-to-warn claims — a ruling could end most of 100,000-plus suits Bayer faces

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The U.S. Supreme Court on Monday heard oral arguments in Monsanto Company v. Durnell, a case that could extinguish more than 100,000 lawsuits alleging that Bayer's Roundup weedkiller caused cancer in users who were never warned of the risk.

At the center of the dispute is whether the Federal Insecticide, Fungicide and Rodenticide Act, or FIFRA, preempts state-level failure-to-warn claims. Bayer, which acquired Monsanto in 2018 for $63 billion, argues that the Environmental Protection Agency has repeatedly reviewed glyphosate — Roundup's active ingredient — and found it does not cause cancer, approving product labels without a cancer warning each time. Because manufacturers cannot alter those federally approved labels without agency approval, Bayer contends, state lawsuits demanding such a warning are barred.

The case began with a 2019 lawsuit from John Durnell of St. Louis. He says he developed non-Hodgkin lymphoma after about 20 years of using Roundup. Court documents say he was the main herbicide applicator for a St. Louis neighborhood association, spraying weeds in local parks for about two decades without protective gear, according to Reuters. In 2023, a jury awarded him $1.25 million in damages, and a Missouri appeals court upheld the verdict in 2025.

Durnell's lawyers argue his claims are not preempted because Missouri law — requiring products to carry adequate warnings — mirrors FIFRA's own prohibition on misbranded pesticide labels. The EPA's registration of Roundup, they contend, does not place its label beyond challenge in court.

The Trump administration has aligned itself with Bayer; Solicitor General D. John Sauer warned in his brief that permitting states to mandate cancer warnings that contradict EPA science would produce a "State-by-State cacophony" drowning out uniform federal standards. President Donald Trump also issued an executive order in February declaring continued glyphosate production critical to national security.

In 2015, the World Health Organization's International Agency for Research on Cancer classified glyphosate as "probably carcinogenic to humans," setting off what one court filing described as a "tidal wave of litigation." The WHO finding ignited what legal filings in the case called a "tidal wave of litigation." While the EPA has consistently held that glyphosate poses no public health risk, critics note that a federal court threw out one of the agency's own health-risk assessments in 2020 after finding its analysis of glyphosate's cancer risk to be defective, according to The New York Times.

In February, with its liability exposure running into the billions, Bayer put forward a proposed $7.25 billion settlement intended to cover tens of thousands of ongoing and anticipated lawsuits. Claims tied to pending appeals or otherwise excluded from the agreement add up to roughly $1 billion, the company has said. A Supreme Court ruling in Bayer's favor would largely render the remaining litigation moot, the company has said.

A decision is expected by the end of June or early July.

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© Quartz