Supreme Court Hears Roundup Cancer Case

The U.S. Supreme Court heard arguments Monday in a case that could significantly impact thousands of lawsuits against Monsanto (now owned by Bayer) over its popular weed killer Roundup, which many claim causes cancer.

At the heart of the dispute is whether federal pesticide laws preempt state failure-to-warn claims. The main plaintiff, John Durnell, won a $1.25 million verdict in Missouri after alleging that 20 years of exposure to glyphosate (Roundup's active ingredient) caused his non-Hodgkin lymphoma.

Justices appeared split on the issue, with arguments focusing on whether federal law should override state-level labeling requirements for herbicides. The Trump administration, which has called Roundup safe, is siding with Bayer in its challenge at the Supreme Court. If successful, thousands of similar lawsuits could be thrown out.

The case has drawn significant attention from various groups filing legal briefs on both sides. Monsanto argues that state labeling requirements should not override federal EPA standards, which currently do not require cancer warnings for glyphosate. The EPA maintains the chemical is unlikely to be carcinogenic, though a World Health Organization agency classified it as a probable human carcinogen in 2015.

Between 2009 and 2019, the EPA repeatedly concluded there is no evidence that glyphosate causes cancer in humans. The agency has allowed glyphosate-based weed killers, including Roundup, to remain on the market without a cancer warning label. This stance contrasts with a 2015 report from the International Agency for Research on Cancer (IARC), which classified glyphosate as 'probably carcinogenic to humans.' A 2025 study found similar findings in lab rats.

Several U.S. lawsuits have used the IARC report to win legal cases claiming that Monsanto failed to warn consumers about cancer risks. One notable case, Hardeman v. Monsanto Co., resulted in an $80 million verdict against Monsanto in 2019. The jury found that Edwin Hardeman, a California man who used Roundup on his properties, proved that the weed killer caused his cancer and that Monsanto failed to warn consumers of its dangers. This finding was upheld on appeal.

In the years since, Monsanto has paid out over $10 billion to settle about 100,000 claims from people who said their health was harmed after exposure to Roundup. However, Monsanto continues to argue that federal law bars states from imposing labeling requirements beyond what the federal government has approved.

A federal judge overseeing thousands of lawsuits alleging Bayer’s Roundup weedkiller causes cancer raised “grave concerns” about a proposed $7.25 billion settlement being rushed through a Missouri state court, questioning whether it could legally bind people who may develop cancer in the future. U.S. District Judge Vince Chhabria said that he had doubts about the state court’s ability to bind future claimants nationwide who were exposed to Roundup but do not yet have cancer.

Chhabria criticized what he called the deal's 'bizarre' opt-out procedures, which require all Roundup users to affirmatively decide to opt out of the settlement over the summer, even if they do not have cancer now. People who develop cancer in the future would still be bound by the deadline and would be swept into the settlement by default.

Despite those concerns, Chhabria said he was not inclined to interfere with the Missouri settlement until it directly impacts the cases pending in his court. The state court settlement is not designed to sweep in those cases, but attorneys representing plaintiffs in the federal court had asked Chhabria to roll back some of the 'oppressive' conditions for opting their clients and future claimants out of the deal.

Outside the court, protesters affiliated with the 'Make America Healthy Again' movement rallied against Bayer and the Trump administration's support for Monsanto. The rally featured speakers from environmental groups and Democratic lawmakers, with signs calling for corporate accountability over pesticide use.