Supreme Court Decision on Roundup Weedkiller Highlights Another Dangerous Pesticide — Paraquat

by Public Health Watch

By Marcus Stern and Daisy Yuhas

This story is part of a series by Public Health Watch and MyRGV.com. Read the first article from this collaboration here.

The U.S. Supreme Court’s 7-2 decision on June 25 shielding the maker of Roundup from claims it failed to warn of the weedkiller’s cancer risk could do more than close the courthouse door on tens of thousands of lawsuits.

It pushes the national fight over a second herbicide — paraquat, linked for decades to Parkinson’s disease — back to the two institutions critics say have spent decades failing to act on it: the U.S. Environmental Protection Agency (EPA) and Congress.

For much of the past decade, courts were the one venue where the makers of widely used pesticides could be forced to answer for hazards that federal regulators didn’t require them to disclose.

The decision on June 25 will largely remove that avenue — jury verdicts that a pesticide manufacturer failed to warn of health hazards, or failure-to-warn claims.

“It’s obviously a devastating loss for victims trying to go through the court process, given what we know about the failure of the regulatory system in the first place,” said Max Sano, senior policy and coalitions associate at Beyond Pesticides, a group seeking to ban toxic chemicals.

“An avenue to justice and accountability has now been shut,” said Geoff Horsfield, legislative director of the Environmental Working Group, which conducts research and advocacy.

The ruling comes in Monsanto Co. v. Durnell, a case that began far from the paraquat fight. John Durnell, a St. Louis resident, developed non-Hodgkin lymphoma after years of using Roundup in neighborhood beautification work and sued Monsanto in Missouri state court in 2019.

A 2023 jury awarded him $1.25 million. The Missouri Court of Appeals affirmed the verdict in February 2025 and the Missouri Supreme Court declined review.

In January, the U.S. Supreme Court agreed to consider Monsanto’s claim that the main federal pesticide law bars failure-to-warn claims like Durnell’s when the EPA has not required a cancer warning.

Monsanto’s argument was that only harms approved by the EPA carry the force of law — so once the agency cleared Roundup without a cancer warning, no state jury could require the company to add one.

Justice Brett M. Kavanaugh, writing for the majority, accepted Monsanto’s argument that the federal pesticide law bars the claim.

Because the EPA had approved Roundup for sale without a cancer warning, he reasoned, a state jury could not require the company to carry one the agency never demanded — a warning, in the court’s words, “in addition to or different from” what federal law requires.

Durnell had argued that a state duty to warn doesn’t add anything “in addition to or different from” federal law; it enforces the same warning obligation the law already imposes, just through a jury rather than the agency.

In a dissenting opinion, Justice Ketanji Brown Jackson wrote:

“In accepting Monsanto’s argument and holding that Durnell’s failure-to-warn claim is preempted, the Court misunderstands (the main federal pesticide law’s) requirements, misinterprets the scope of (its) preemption, and ultimately leaves Durnell without a remedy for the significant harms he has suffered.”

Hammering out the warning requirements for a pesticide is a long process of study and review, with manufacturers providing much of the data and studies, and the EPA the review. Once this back and forth is completed, the EPA approves what is called the pesticide’s label.

The label isn’t marketing glued to the jug. It is a legal document — the detailed instructions, use restrictions and health and safety warnings that the EPA reviews and must approve before a product can be sold.

The agency must approve what the label says, including which hazards it flags, and a manufacturer generally cannot add, drop or alter a warning without the agency’s sign-off. Selling a pesticide with a label that departs from the approved version can expose a company to civil and even criminal penalties.

In practice, the label is the law — which is why who controls its wording determines who can be held to account for what it leaves out.

The statute underlying the pesticide cases is the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), which governs the registration, sale, and use of pesticides and is administered by the EPA. Under FIFRA, no pesticide may be sold until the EPA approves it and signs off on its label.

On June 25, the justices sided with Monsanto’s central argument: Once the EPA approves a pesticide’s label without a particular warning, a state jury cannot hold the maker liable for leaving it off.

Horsfield, of the Environmental Working Group, said the Supreme Court has made a mistake in assuming it can “rely on EPA as some grand arbiter of science. We have seen time and time again that the EPA receives information and either doesn’t act on it or ignores it.”

Even as the EPA has maintained that glyphosate, the active ingredient in Roundup, is not likely to cause cancer, juries have repeatedly sided with users who said years of exposure to the weedkiller gave them non-Hodgkin lymphoma.

In overturning Durnell’s $1.25 million verdict, the court held that FIFRA bars failure-to-warn suits like his.

The stakes are enormous. The German company Bayer AG, which inherited the Roundup litigation when it bought Monsanto in 2018, has already paid roughly $11 billion to settle claims from users who say the weedkiller caused their cancer, resolving nearly 100,000 cases by the company’s count while about 61,000 remain pending.

In February, Monsanto proposed a separate $7.25 billion class settlement to cover most of the rest — current and future claimants alike — with a hearing on the deal scheduled for July 9.

The June 25 ruling reshapes that calculus. By foreclosing the failure-to-warn theory that anchored the largest jury verdicts, it strips the remaining plaintiffs of their most potent claim and strengthens Bayer’s hand, both in the cases still moving through the courts and in pressuring holdouts to accept the settlement rather than go it alone.

The high court’s ruling extends well beyond Roundup. The clearest target is paraquat, the herbicide at the center of more than 6,000 federal claims — and thousands more in state courts — brought by farmers and applicators who say it caused their Parkinson’s disease.

Those lawsuits, consolidated before a federal judge in southern Illinois, rest on the same theory the court rejected Thursday: that the manufacturers, Syngenta and Chevron, failed to warn of a risk the EPA never required on the label.

The legal architecture is identical — the same statute, the same preemption clause, the same missing federal warning — and both sides in the paraquat litigation have told the court that the Durnell ruling could determine whether those claims survive.

In April, Syngenta announced it would stop production of paraquat, claiming the decision was made “solely for commercial reasons,” as Public Health Watch reported this month.

The paraquat litigation against Syngenta and Chevron also illustrates what several advocates see as a strength of failure-to-warn litigation: a means for extracting corporate knowledge about a product’s possible dangers.

For example, “Syngenta and other corporations knew about the harms of some of these products but that would not necessarily have come to light without the legal accountability,” said Sano of Beyond Pesticides.

The June 25 ruling all but forecloses that route for the failure-to-warn claims at the heart of the paraquat litigation. This sends a long-stalled campaign to rein in the chemical back to an agency and a Congress that have repeatedly declined to ban it.

For the thousands of people who are suing Chevron, Syngenta and Bayer, there may still be a way forward.

“It’s not the end of the road. Technically people still have the ability to file lawsuits, but that burden is much higher,” Horsfield added.

Attorney Scott Hendler agreed. Hendler is CEO and managing attorney of Hendler Flores Law, which represents plaintiffs in both glyphosate and paraquat litigation.

“There are other claims that can still proceed … We don’t intend to abandon these clients.”

For example, many plaintiffs can still sue over design or manufacturing defects or fraudulent concealment of data.

But legal teams will need to pivot.

“A lot of lawyers bringing these cases, looking for the path of least resistance — meaning failure to warn — may drop these cases and walk away from them,” he added.

The one path the Supreme Court left fully open for pesticide regulation is the bluntest: A state remains free to outlaw a pesticide outright. So far, only one has done so with paraquat.

In late May, Vermont became the first state in the nation to ban it — even as more than 70 countriesalready had, among them China, which bars paraquat from its own farms yet, through a state-owned conglomerate, owns Syngenta itself.

The court has made the primary arbiters of paraquat’s fate the same two institutions that have left it on the market for half a century — an EPA whose safety reviews lean on industry-generated data, and a Congress where bills to restrict the chemical keep dying within reach of the lobbyists working against them.

But the paraquat plaintiffs have one argument the Roundup plaintiffs lacked. The EPA repeatedly and explicitly studied glyphosate’s cancer risk and pronounced it unlikely.

On paraquat, the EPA never made the equivalent finding. It concluded only that the evidence was “insufficient” to link the herbicide to Parkinson’s — and in 2025, facing a legal challenge, it withdrew even that interim decision, reopened the review and has not issued a revised finding since.

That means the EPA has not issued a standing finding, one way or the other, on whether there is a link between paraquat and Parkinson’s.

Parkinson’s claimants could therefore argue that because the EPA never decided the Parkinson’s question, its approval of the label cannot preempt a jury from making that link.

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This article was originally published by Public Health Watch, a nonprofit investigative news organization. Find out more at publichealthwatch.org.  

Marcus Stern is a Pulitzer Prize- and Emmy Award-winning journalist with three decades of Washington reporting experience and another decade as an independent journalist based in Georgia and Florida.

Daisy Yuhas, contributing writer, is an award-winning science journalist and editor based in Austin, Texas.