Supreme Court Rejects Lawsuit Alleging Roundup Weedkiller Caused Cancer

The Supreme Court on Thursday sided with the manufacturer of the weedkiller Roundup, overturning a jury award for a Missouri man who claimed the widely used herbicide caused cancer in a decision that could have sweeping impacts on thousands of other Americans who similarly claim the product sickened them.

In the 7-to-2 decision, written by Justice Brett M. Kavanaugh, the majority found that a federal law that regulates pesticides barred the Missouri man’s lawsuit.

Justice Kavanaugh wrote that the Missouri case would “require a cancer warning on Roundup’s label,” which would directly conflict with the label required by the federal Environmental Protection Agency. Because of this conflict, he wrote, federal law “expressly pre-empts” the Missouri man’s claim.

The dispute focused on a single case, a $1.25 million award for John Durnell, a gardener in St. Louis who had used Roundup for decades and claimed that years of exposure to the product led him to develop non-Hodgkin lymphoma, a blood cancer. Mr. Durnell claimed that the company had failed to warn consumers of the dangers of the product.

The ramifications of the decision could be enormous, potentially jeopardizing thousands of lawsuits pending in state and federal courts against Bayer, the German company that acquired Roundup’s original maker, Monsanto, in 2018.

The legal question before the justices focused on a narrow slice of the broader litigation: whether Bayer can be sued in state-level courts given that a federal agency decided not to issue a warning label for the weedkiller.

The Environmental Protection Agency, which is in charge of labeling pesticides throughout the country, has determined Roundup is safe. Bayer claims that the finding, which allows Roundup to be sold without a warning label, should override claims by Mr. Durnell and others that under state laws, they were injured by the product.

The Trump administration joined the case on Bayer’s side, reversing the position taken by the Biden administration. The Trump administration’s support for the Roundup manufacturer has been controversial among the Make America Healthy Again movement, whose activists had largely supported the president’s political rise.

Government lawyers asserted that once the E.P.A. determined Roundup was safe, Bayer was in fact required to abide by the agency’s decision in its product labeling.

If the company had tried to unilaterally change the product’s label, they argued, it would have violated the Federal Insecticide, Fungicide and Rodenticide Act.

Roundup, which was created by Monsanto in the 1970s, is one of the most popular weedkillers in the world. But concerns over one of its active ingredients — a chemical called glyphosate that is absorbed by plants, traveling into their roots and blocking an enzyme used for their growth — have prompted one of the biggest waves of class-action lawsuits in U.S. history.

Evidence in lab animals, along with more limited evidence in humans, has shown a link between glyphosate and cancer, and a 2015 report by the World Health Organization’s International Agency for Research on Cancer classified it as “probably carcinogenic to humans.”

The E.P.A. has studied the chemical and determined a cancer warning was not necessary. In February 2020, the agency announced findings that “there are no risks of concern to human health when glyphosate is used in accordance with its current label” and that the chemical was “unlikely” to cause cancer in humans.

After a court challenge, the E.P.A. withdrew those findings and the chemical’s safety currently remains under formal review.

In his lawsuit, Mr. Durnell said the company should be liable for failing to warn users about the risks of developing non-Hodgkin lymphoma from exposure to glyphosate.

In 2023, a jury in the Circuit Court of the City of St. Louis, a state court, sided with Mr. Durnell. The company appealed the case, which eventually landed at the Supreme Court.

Julie Tate contributed research.