The United States Supreme Court ruled 7–2 on Thursday in favour of Bayer, the German chemicals and pharmaceuticals giant, effectively blocking thousands of lawsuits filed by people who claim that the Roundup weedkiller caused their cancer. The decision overturns a jury verdict in Missouri that had awarded more than one million dollars to John Durnell, a farmer who argued that roughly two decades of exposure to Roundup caused him to develop non-Hodgkin's lymphoma, a form of blood cancer. The ruling is expected to lead to the dismissal of tens of thousands of similar pending cases across the country.

Crucially, the court did not rule on whether Roundup's active ingredient, glyphosate, actually causes cancer. Instead, the majority held that federal regulatory authority — specifically the approval framework of the Environmental Protection Agency (EPA) — takes precedence over individual US states' consumer protection laws. Because the EPA does not require a cancer warning on Roundup's label, state-level lawsuits arguing that such a warning was missing were found to impose requirements that conflict with federal rules and are therefore inadmissible. The two dissenting justices argued that an EPA approval should not automatically relieve a manufacturer of its broader duty to warn consumers of potential hazards.

The scientific picture, however, remains contested. In 2015, the International Agency for Research on Cancer, an arm of the World Health Organization, classified glyphosate as a "probable human carcinogen," based on peer-reviewed animal, toxicological, and epidemiological studies. Critics of the ruling also note that one key study frequently cited to support glyphosate's safety was recently retracted over ethical concerns and research misconduct — concerns that only came to light through the litigation process itself. Supporters of the decision, including Bayer, argue that it restores regulatory clarity and defers appropriately to scientific bodies designated to assess such risks.

Bayer, headquartered in Leverkusen, Germany, acquired Roundup's original manufacturer Monsanto in 2018 for 63 billion dollars — a deal that immediately drew warnings about the scale of its legal exposure over glyphosate. The company has since paid roughly ten billion dollars to settle earlier lawsuits and had set aside a further eight billion dollars for ongoing cases. Following Thursday's ruling, Bayer's share price jumped around 20 percent to a four-month high, heading for its largest single-day gain in approximately 23 years.

For cancer patients and their advocates, the ruling raises troubling questions about the limits of legal recourse when regulatory assessments and independent scientific findings diverge. Glyphosate remains the world's most widely used pesticide active ingredient and, while Bayer no longer sells Roundup directly to private consumers in the United States, it continues to be sold commercially and applied across more than 300 million acres of American farmland. Environmentalists have long warned that beyond any cancer risk, glyphosate's near-total destruction of plant life also threatens biodiversity by eliminating food sources for birds and insects.