Supreme Court Weighs Monsanto's Roundup Cancer Warning Case: What It Means for Pesticide Regulation

The U.S. Supreme Court heard oral arguments on Monday in Monsanto Company v. Durnell, a landmark case that could redefine the balance of power between state and federal authorities over cancer warnings on pesticide labels.

At the heart of the dispute is whether states can require warnings about cancer risks from glyphosate—the active ingredient in Monsanto’s Roundup weed killer—despite the Environmental Protection Agency’s (EPA) conclusion that the chemical does not cause cancer.

In 2019, John Durnell filed a lawsuit against Monsanto Co., alleging that exposure to glyphosate led to his development of non-Hodgkin’s lymphoma. In 2023, a jury sided with Durnell, awarding him $1.25 million after determining that Monsanto failed to adequately warn users of the alleged cancer risk.

Monsanto has appealed the verdict, arguing that federal law under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) preempts state courts from imposing warning labels that contradict EPA assessments. The company contends that since the EPA has not mandated a cancer warning, states cannot legally require one, and thus, lawsuits like Durnell’s should not proceed.

Key Legal Arguments Before the Supreme Court

The case centers on whether states can act independently when new scientific evidence emerges that challenges EPA rulings. Several justices expressed concerns about the implications of Monsanto’s argument:

• Chief Justice John Roberts questioned whether states would be powerless to act if the EPA fails to update warnings despite new evidence. “The states cannot do anything?” he asked.
• Justice Ketanji Brown Jackson raised concerns about how emerging science could render a product “misbranded” if its labeling no longer reflects current safety assessments.
• Justice Brett Kavanaugh warned of a potential “due process problem,” where companies could face liability for complying with EPA directives.

Sarah Harris, a deputy solicitor general for the Justice Department, countered that allowing states to impose their own warnings could lead to a patchwork of conflicting regulations. The department filed an amicus brief in December arguing that FIFRA’s uniformity requirement vests the EPA with sole authority over pesticide warnings.

“If States can compel petitioner to add a cancer warning—contrary to EPA’s scientific judgments—States could drown EPA’s approved warnings in a sea of local health and environmental concerns.”

Durnell’s legal team argued that the EPA had overreached its regulatory authority and that courts—particularly state courts—should play a stronger role in safeguarding public health and environmental safety. However, several justices questioned whether this approach could create a fragmented regulatory landscape across the U.S.

The Supreme Court’s decision, expected later this year, will have far-reaching consequences for pesticide regulation, corporate liability, and the authority of state versus federal agencies in consumer safety matters.