Does Weed Killer Cause Cancer? Roundup of the Epic Battle for Truth

For fifty years, we were told the science on glyphosate was settled, but Monsanto's unsealed internal documents and scientific evidence retraction are now telling a much darker story.

"A Monsanto scientist named William Heydens suggested that the company could "ghost-write" a new research paper to counter the WHO's cancer findings." 

What does "probably carcinogenic" actually mean? It suggests there's strong evidence of carcinogenicity in experimental animals and limited evidence in humans. The IARC's finding was based on publicly available scientific literature, and it contrasted sharply with assessments from other regulatory bodies, like the U.S. Environmental Protection Agency (EPA), which have generally maintained that glyphosate is not likely to be carcinogenic to humans at current exposure levels.

Chemical Manufacturers Ghostwrite Studies as “Evidence”

The divergence in scientific opinion isn't just a matter of differing interpretations; it’s entangled in allegations of corporate influence and false safety studies. Lawsuits against the manufacturers of glyphosate-based products have brought to light internal company documents suggesting that some scientific papers supporting glyphosate’s safety were, in fact, heavily influenced or even drafted by company scientists, then attributed to independent academics.

The "Independent" Study That Wasn't

The paper, titled Safety Evaluation and Risk Assessment of the Herbicide Roundup and Its Active Ingredient, Glyphosate, for Humans, was presented as an independent review by three respected outside scientists: Gary M. Williams, Robert Kroes, and Ian C. Munro. Because it didn't come directly from Monsanto, it carried immense weight with the EPA and other global agencies.

However, during the massive discovery process of the recent lawsuits, internal Monsanto emails came to light. In one 2015 email, a Monsanto scientist named William Heydens suggested that the company could "ghost-write" a new research paper to counter the WHO's cancer findings. He explicitly wrote:

"Recall that is how we handled Williams, Kroes and Munro 2000."

Other unsealed documents revealed that Monsanto employees actually drafted sections of the paper, edited the content, and even organized the "independent" scientists who put their names on it. One internal email even praised a group of Monsanto scientists for their "hard work" and "perseverance" in getting this "independent" assessment published.

The 2025 Retraction: Oops, Roundup Might Be Harmful After All

For years, despite these revelations, the study remained in the official scientific record. That changed just recently. In December 2025, the journal Regulatory Toxicology and Pharmacology officially retracted the Williams et al. study.

The journal’s editor-in-chief cited "serious ethical concerns" and a lack of transparency regarding Monsanto’s involvement. The retraction notice pointed out several critical issues:

• Failure to disclose that Monsanto staff helped write the article.
• Potential undisclosed financial compensation to the authors.
• Reliance on unpublished internal Monsanto data while ignoring independent studies that showed potential harm.

For years, the EPA has relied on this specific paper to maintain its stance that glyphosate is safe. In fact, even as recently as 2020, the EPA’s safety assessments were still heavily influenced by the conclusions laid out in this 2000 ghostwritten study. We’ve written about the problems with the EPA before, check out The EPA is Evidently Corrupt.

This gag law would allow companies to sue journalists, scientists, or even everyday citizens for defamation if they claim a pesticide or practice is unsafe without meeting a strict, industry-friendly definition of "scientific facts.

By striking this study from the record, the scientific foundation the EPA usedto approve Roundup has effectively crumbled. This is why the industry is now moving so fast to pass immunity laws; they know that without these "hallmark" studies to lean on, their defense in an open courtroom becomes much harder to maintain.

Weed Killer Manufacturers Seeking Legal Immunity

Facing a mountain of multi-billion-dollar verdicts, Bayer and other chemical giants have launched an aggressive legislative campaign. They aren't just trying to win cases anymore; they are trying to make it illegal to sue them in the first place.

The strategy is to lobby state legislatures to pass "preemption" bills. These laws essentially state that if the EPA has approved a product’s label and that label doesn't require a cancer warning, then a manufacturer cannot be held liable under state law for a "failure to warn."

If this sounds familiar, it’s because it mirrors the legal protections given to vaccine manufacturers under the 1986 National Childhood Vaccine Injury Act. The goal is to create a "liability shield" that prevents individual citizens from bringing their grievances before a jury.

Pesticide Liability Bills

The chemical industry has founded groups like the Modern Ag Alliance to lead this charge, arguing that these lawsuits threaten the very future of American farming by potentially forcing "crop protection tools" off the market.

While states like Georgia and North Dakota have already slammed the door shut on certain lawsuits, North Carolina is currently at a tipping point. As of January 2026, the North Carolina Farm Act of 2025 (Senate Bill 639) is sitting in a closed-door "conference committee" where lawmakers are deciding the fate of Section 19.

This controversial provision, often called a pesticide liability shield, would effectively grant chemical manufacturers immunity by stating that an EPA-approved label is enough to protect them from "failure to warn" lawsuits. If this passes, North Carolinians who develop illnesses linked to weed killers could be blocked from seeking justice in state courts, regardless of what independent science reveals about the product’s safety.

Florida is pushing the envelope even further with a different kind of legal threat. As of early 2026, Florida lawmakers have introduced a "disparagement" provision that could give agricultural and chemical producers the right to sue anyone who publicly criticizes their products or farming practices. This gag law would allow companies to sue journalists, scientists, or even everyday citizens for defamation if they claim a pesticide or practice is unsafe without meeting a strict, industry-friendly definition of "scientific facts." 

The Supreme Court Blanket Immunity from Liability

This state-by-state strategy is the "Plan B." The "Plan A" is happening at the highest level. On January 16, 2026, the U.S. Supreme Court agreed to hear a landmark case (arising from a Missouri verdict) that could settle this once and for all.

Bayer is asking the Court to rule that the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) preempts state law. If the Supreme Court agrees, it could effectively grant "blanket immunity" to pesticide manufacturers nationwide, rendering the thousands of pending lawsuits and the billions in potential payouts null and void.

Making Informed Choices for Your Yard and Health

So, what does all this mean for you and your lawn? The scientific and legal debates around chemicals like glyphosate are complex and continue to evolve. There isn't a simple "yes" or "no" answer that satisfies everyone, and different regulatory bodies worldwide still hold differing opinions.

Given this landscape, adopting a cautious approach can empower you to protect your health and the environment.

Consider these steps:

• Read Labels Carefully: Understand the active ingredients. We recommend cross-referencing them with the Beyond Pesticides Gateway.
• Explore Organic Options: A growing number of organic herbicides are available. Our services in the Raleigh-Durham area use citric acid, oils, and soaps instead of harsh synthetics.
• Improve Soil Health: A healthy, dense lawn is naturally more resistant to weeds and pests. Focus on proper watering, fertilizing with organic compost, and aerating your soil.
• Stay Informed: Keep an eye on advocates like Kelly Ryerson (The Glyphosate Girl) who track these legal and scientific updates in real-time.
• Reduce Exposure: Find out when and what kind of weed treatments happen in your community schools, parks and neighborhoods. (Check out our post: Is Your HOA Using Toxic Lawn Care Products?) 
  

Ultimately, the decision of what to use in your yard is a personal one. A beautiful lawn shouldn't come at the expense of your peace of mind.