WASHINGTON - The Supreme Court on Monday wrestled with whether federal law preempts judges and juries from weighing claims from tens of thousands of cancer patients that the chemical giant Monsanto failed to warn them about alleged cancer risks from the popular weed killer Roundup.

The case argued before the justices dealt with a prosaic legal question, but one with enormous consequences. The court will determine the fate of one of the largest waves of product liability litigation in the nation’s history. Billions of dollars are at stake, as well as the future of a chemical the nation’s largest farm group says is so important that ending its use would threaten America’s food supply but many environmentalists assert is toxic.

The justices seemed to lean toward restricting the lawsuits, but they asked tough questions of both sides and the outcome remains unclear.

At the heart of the case is glyphosate, the active ingredient in Roundup and other name brands that has been used as an herbicide since the 1970s. Roundup is one of the most widely used weed killers in the world.

The Environmental Protection Agency has found repeatedly over decades that glyphosate does not cause cancer in humans, but in 2015 a prominent cancer research group associated with the World Health Organization and United Nations determined glyphosate was “probably carcinogenic to humans.”

The finding led some countries to ban the herbicide and touched off a flood of lawsuits against Monsanto. The company, which is now owned by the German conglomerate Bayer, denies Roundup causes cancer. More than 100,000 lawsuits have been filed in American courts, and Bayer has spent about $11 billion on settlements to date.

The case before the Supreme Court involves one of those lawsuits.

John Durnell sued Monsanto in Missouri state court in 2019, alleging exposure to Roundup had caused his non-Hodgkin lymphoma, a form of blood cancer. Durnell used Roundup to spray weeds in parks near his St. Louis home for two decades before his diagnosis.

Durnell’s suit claimed Monsanto had a duty to warn consumers that Roundup was a cancer risk.

Durnell points to findings that Monsanto relied on fraudulent studies to obtain Roundup’s approval. The leaders of the laboratory that performed the study were later convicted of fraud. The fraud became public in 1976, but Monsanto did not disclose it to customers subsequently.

A Missouri jury ruled for Durnell, awarding him $1.25 million in damages. An appeals court rejected Monsanto’s appeal, before the company eventually asked the Supreme Court to take up the case.

Such lawsuits have prompted Monsanto to remove Roundup from the consumer market, but it is still available to farmers. Monsanto says allowing additional suits to go forward could prompt additional action.

“To remove glyphosate from the market would pose an immediate, devastating risk to America’s food supply,” the bureau wrote. “Farmers depend on this safe herbicide to support high-yield food and fiber production, season after season. Glyphosate is used on roughly 300 million acres of U.S. farmland.”

Some farm workers’ groups, cancer prevention organizations and environmentalists say Roundup poses substantial risks and should be labeled as causing cancer. Some rallied outside the Supreme Court Monday.

“Cancer is an epidemic, afflicting more than 1 in 3 Americans within their lifetimes,” the Center for Food Safety and other groups wrote in a friend-of-the-court brief. “The Court should not afford Monsanto immunity for its products’ risks … and deny Americans their right to know the risks of an inherently dangerous product.” (Source: The Washington Post)

Story Date: April 28, 2026