A retracted study on Roundup reignites debate over its potential cancer risk

A scientific journal has retracted a bedrock study which found that glyphosate – the active ingredient in one of the most widely used herbicides on the planet – does not pose a human health risk, igniting a fresh debate over the chemical’s possible link to cancer.

Scientists and regulators have worked for years to determine whether glyphosate – the active ingredient in Roundup, which was produced by Monsanto until the company was acquired by Bayer in 2018 – causes cancer. European and U.S. officials have not classified it as a carcinogen, while the World Health Organization deemed it “probably carcinogenic to humans” in 2015.

Last Friday the scientific journal Regulatory Toxicology and Pharmacology retracted a 2000 study that concluded “under present and expected conditions of new use, there is no potential for Roundup herbicide to pose a health risk to humans.”

The retraction from the co-editor in chief said evidence suggests that Monsanto employees “may have contributed to the writing of the article without proper acknowledgment as co authors,” the study’s authors may have been paid by Monsanto without disclosing it and that the findings about its cancer risk “are solely based on unpublished studies from Monsanto.”

Noting that the paper “had a significant impact on regulatory decision-making regarding glyphosate and Roundup for decades,” the journal concluded that it has “lost confidence in the results and conclusions of this article, and believes that the retraction of this article is necessary to maintain the integrity of the journal.”

The Environmental Protection Agency, which is slated to announce an updated human health risk assessment for glyphosate next year, cited the paper in its 2016 review of glyphosate. It later determined that the pesticide ingredient was “not likely to be carcinogenic to humans.”

But EPA press secretary Brigit Hirsch said in a statement that retraction would not affect its stance because it does not directly rely on review articles to inform its pesticide risk assessments. She added that the study was used as a source to find other relevant studies and ensure that the agency had the most complete database for health risk assessment for glyphosate, but was not used on its own.

“The retraction of this publication has no impact on EPA’s glyphosate assessment, which has historically reviewed more than 6,000 individual studies across all disciplines, including human and environmental health,” Hirsch said.

Monsanto’s influence over the study was discovered through internal emails during federal litigation against the company in 2017. Bayer has spent roughly $10 billion to settle lawsuits arguing that the company did not warn customers about the negative health impacts of using Roundup.

In a statement, Bayer defended the chemical’s safety and said Monsanto’s involvement was appropriately cited in the acknowledgments.

“Glyphosate is the most extensively studied herbicide over the past 50 years. Thousands of studies have been conducted on the safety of glyphosate products,” said Bayer spokesman Brian Leake. “The vast majority of published studies on glyphosate had no Monsanto involvement.”

But advocates and scientists say that the study, one of the most-cited papers on glyphosate safety, underpinned federal regulations for the pesticide and that the retraction raises questions about the scientific literature that followed it.

Scientists who have studied the health effects of glyphosate on humans said the retracted study led people to prematurely believe in glyphosate’s safety and dissuade policymakers from regulating it.

“It got us off on the wrong course,” said Brenda Eskenazi, a professor at the University of California at Berkeley’s school of public health.

Alexander Kaurov and Naomi Oreskes, who requested the retraction, published research in September that found the paper is in the top 0.1% of cited academic literature on glyphosate. Oreskes, a professor of the history of science at Harvard University, said the manipulation and distortion of the scientific literature means that the “very foundation for decision-making has been undermined.”

“Even if EPA doesn’t rely on this one, it relies on many other papers that rely on this review,” said Kaurov, a PhD candidate at the School of Science in Society at Victoria University of Wellington. “It’s impossible to come up with any decision without relying on studies that rely on this review.”

The controversy over the study comes as the Trump administration has backed Bayer’s efforts to obtain legal immunity from these lawsuits.

The Office of Solicitor General filed a brief in support of Bayer on Tuesday, arguing that failure-to-warn lawsuits in state courts are preempted by federal law. Bayer is challenging a Missouri failure-to-warn lawsuit, where a jury awarded $1.25 million to a man who claimed he developed non-Hodgkin’s lymphoma from exposure to Roundup.

“For decades, EPA has classified glyphosate as a chemical that is not likely to be carcinogenic in humans, and the agency has approved hundreds of labels for Roundup and other glyphosate-based products without requiring a cancer warning,” the brief stated.

Bayer has also sought to obtain immunity from legal liability connected to glyphosate on the state level and in Congress.

At the same time, debates about glyphosate’s potential health risks have revealed deep divisions between the Trump administration and its “Make America Healthy Again” allies.

Health and Human Services Secretary Robert F. Kennedy Jr., whose department does not directly oversee pesticide regulation, has criticized them for years. He tweeted last year that glyphosate was “one of the likely culprits in America’s chronic disease epidemic” and, in a social media post five years ago, called Monsanto “the enemy of every admirable American.”

As an environmental lawyer, Kennedy was part of a team that in 2018 won a $289 million judgment against Monsanto over claims the weed killer caused cancer.

The administration’s backing of Bayer immunity push has drawn criticism from MAHA activists.

Vani Hari, an author, activist and Kennedy ally known as the “Food Babe,” said that if Bayer receives a liability shield, MAHA activists will shift their support, impacting leaders and future elections.

“We want President Trump to uphold his promise to safeguard American families from toxic pesticides,” Hari said.