The Monsanto Papers: What Internal Documents Revealed About Glyphosate Research, and Why a Key Safety Review Was Retracted

Headlines have claimed for years that “secret documents” prove Monsanto knew decades ago that glyphosate, the active ingredient in Roundup, causes cancer. The reality is more specific and, in some ways, more important. Documents released through litigation since 2017 show how the company worked to shape scientific literature and regulatory debates about its best-selling herbicide, including by ghostwriting a review article that was cited for decades as an independent assessment of glyphosate’s safety. In December 2025, that review was formally retracted.

At the same time, the documents do not by themselves settle whether glyphosate causes cancer, a question on which scientific bodies still disagree. This article explains what the early regulatory history shows, what the “Monsanto Papers” revealed, why the retraction matters, what critics of the retraction argue, and what the episode means for trust in how chemicals are regulated.

The Early Regulatory History

Monsanto introduced glyphosate commercially in 1974. As part of registration, companies submit toxicology studies to the U.S. Environmental Protection Agency, including long-term studies in rodents designed to detect cancer.

A mouse study submitted in the early 1980s found a small number of rare kidney tumors in male mice given glyphosate. In 1985, an EPA panel reviewing the data classified glyphosate as a possible human carcinogen, then called Group C. The classification became the source of later claims that Monsanto “knew” about a cancer link in the 1980s.

The story did not end there. The tumor findings were contested, partly because the number of tumors was small and statistical significance was debatable. A re-examination of the tissue slides, which Monsanto commissioned, reported finding a kidney tumor in a control animal as well, weakening the apparent treatment effect. After further review, in 1991 the EPA reclassified glyphosate as Group E, “evidence of non-carcinogenicity for humans,” while noting that the classification was based on the available evidence and could change with new data.

Critics have long argued that the reclassification was too readily accepted and that industry influence shaped it. Supporters of the decision note that it reflected scientific review of the full dataset. Either way, the record shows a genuine scientific dispute about animal data in the 1980s, not a hidden finding that glyphosate definitively caused cancer.

What the “Monsanto Papers” Revealed

After the World Health Organization’s International Agency for Research on Cancer classified glyphosate as “probably carcinogenic to humans” in 2015, thousands of people with non-Hodgkin lymphoma sued Monsanto. In the consolidated federal litigation in California, many internal company documents were produced in discovery, and beginning in 2017 plaintiffs’ lawyers and others made a large number of them public. The consumer advocacy group U.S. Right to Know has compiled many of these documents, which became known as the Monsanto Papers.

The documents covered several areas:

Ghostwriting. Emails indicated that Monsanto employees drafted or substantially shaped scientific articles that were published under the names of outside academic scientists, without the company’s role being disclosed. One email, describing a plan for a later paper, referred to the approach used for the 2000 Williams, Kroes, and Munro review as a model.

Strategy around IARC. Internal communications described plans to respond to and discredit the anticipated IARC classification, including by organizing outside experts and publications.

Interactions with regulators. Some emails described contacts between Monsanto staff and EPA officials, which critics cited as evidence of inappropriate closeness and which the agency and company defended as routine communication with a regulated party.

Internal scientific discussions. Some documents showed company scientists discussing gaps in testing of formulated Roundup products, as distinct from glyphosate alone, and debating whether additional studies were needed.

Bayer, which acquired Monsanto in 2018, has said the documents were taken out of context and that the safety of glyphosate is supported by a large body of independent research and regulatory reviews.

The 2000 Review and Its 2025 Retraction

In April 2000, Regulatory Toxicology and Pharmacology published a comprehensive review titled “Safety evaluation and risk assessment of the herbicide Roundup and its active ingredient, glyphosate, for humans,” by Gary Williams of New York Medical College, Robert Kroes of Utrecht University, and Ian Munro of Cantox Health Sciences International. It concluded that glyphosate did not pose a health risk to humans under normal conditions of use. For years, it was among the most cited references on glyphosate safety and was referenced in regulatory documents.

The Monsanto Papers indicated that Monsanto employees had contributed substantially to the article without being named as authors. As Retraction Watch reported, the journal retracted the review in late 2025, eight years after the documents surfaced in court, following formal requests from researchers who had studied the paper’s influence. Kroes had died in 2006 and Munro in 2011.

According to reporting by ScienceAlert, the retraction notice by co-editor-in-chief Martin van den Berg said several critical issues undermined the article’s academic integrity, including that its conclusions on cancer and genetic toxicity were based solely on unpublished studies from Monsanto and omitted other long-term studies completed at the time. The notice said the editor had tried to contact Williams, the only surviving author, without receiving a response. The New Lede highlighted internal emails in which Monsanto staff described the paper as expected to become “the” reference on Roundup and glyphosate safety.

Not everyone agrees with the retraction

The decision has been contested. Retraction Watch reported in June 2026 that a group of 66 researchers had written an editorial calling on the journal to reverse the retraction, with the campaign’s leader arguing that the rationale was not defensible and the ghostwriting concerns were weak. The journal’s co-editor-in-chief said it would not reverse the decision, and the publisher was investigating other glyphosate papers over similar concerns.

What the retraction does and does not mean

A retraction means a journal no longer stands behind a paper’s integrity. It does not, on its own, show that the paper’s conclusions were wrong or that glyphosate causes cancer. Regulatory assessments in the United States and Europe draw on hundreds or thousands of studies, including guideline toxicology studies submitted by manufacturers, published research, and epidemiological data. Supporters of glyphosate’s regulatory status argue that removing one review changes little in that larger body of evidence. Critics respond that the review shaped how evidence was summarized and perceived for decades, and that its retraction is a reason to re-examine how regulators weigh industry-controlled data.

How Regulators Use Industry Studies

Part of what makes the Monsanto Papers significant is that pesticide regulation everywhere relies heavily on studies paid for by manufacturers. This is by design: companies seeking to sell a product are required to fund the extensive toxicology and environmental studies needed to evaluate it, rather than taxpayers. Those studies must follow Good Laboratory Practice standards, which govern documentation, quality assurance, and data integrity, and regulators review the raw data rather than relying on summaries.

The system has strengths and weaknesses. Guideline studies are standardized and often more detailed than academic research. But because many have historically been confidential, outside scientists could not easily scrutinize them, and published reviews written or shaped by companies could influence perceptions without disclosure. The Monsanto Papers highlighted the second risk.

The European Union responded in part with a transparency regulation, Regulation (EU) 2019/1381, which since 2021 has required the European Food Safety Authority to make studies supporting applications publicly available, with limited confidentiality exceptions, and requires notification of commissioned studies so that unfavorable studies cannot be quietly omitted. Proposals to improve transparency in the United States have been discussed, but the U.S. system still treats many study details as confidential business information.

Common claim	What the record shows
“Monsanto knew glyphosate causes cancer in the 1980s”	An EPA panel classified it as a possible carcinogen in 1985 based on contested mouse data; EPA reclassified it in 1991 after further review.
“Monsanto ghostwrote safety research”	Internal emails indicate employees substantially contributed to published reviews without disclosure; a key 2000 review was retracted in 2025.
“The retraction proves glyphosate causes cancer”	No. A retraction addresses integrity of one paper; the cancer question rests on the full body of evidence and remains disputed.
“Regulators relied entirely on Monsanto”	Regulators reviewed many studies, including industry guideline studies and published research; critics argue industry data carried too much weight.

Where the Cancer Question Stands

The Monsanto Papers and the retraction have not resolved the scientific question at the center of the litigation. The International Agency for Research on Cancer classified glyphosate in 2015 as probably carcinogenic, citing limited human evidence for non-Hodgkin lymphoma, sufficient animal evidence, and strong mechanistic evidence, as summarized in The Lancet Oncology. The U.S. EPA and European regulators have concluded that glyphosate is unlikely to pose a cancer risk at expected exposures; the EPA’s registration review is ongoing after a 2022 court ruling sent parts of its human health analysis back to the agency.

Human studies remain mixed. The Agricultural Health Study’s 2018 analysis of more than 54,000 pesticide applicators found no association between glyphosate use and non-Hodgkin lymphoma. A 2019 meta-analysis focusing on the highest exposure groups reported a 41 percent increased risk. Neither the original 2000 review nor its retraction changes these primary studies.

The Legal Consequences

The Monsanto Papers played a prominent role in the Roundup lawsuits. In 2018, a California jury awarded damages to a school groundskeeper with non-Hodgkin lymphoma, the first of several large verdicts; amounts were later reduced on appeal. In 2020, Bayer announced a settlement of roughly $10 billion to resolve many existing claims while new claims continued. In June 2026, the U.S. Supreme Court ruled 7 to 2 in Monsanto Co. v. Durnell that federal pesticide law preempts state-law claims seeking cancer warnings beyond those the EPA has approved, significantly limiting future failure-to-warn lawsuits. The ruling addressed legal authority over labels, not the science of glyphosate and cancer.

What Glyphosate Is and Why It Matters So Much

Glyphosate kills plants by blocking an enzyme in the shikimate pathway, which plants use to make certain amino acids. Animals do not have this pathway, which is one reason glyphosate was long considered to have low toxicity for people. It is a broad-spectrum herbicide, killing most plants it contacts, and is used on farms, in forestry, along roads and railways, in parks, and in home gardens.

Its use expanded dramatically after the introduction of glyphosate-tolerant genetically engineered crops in 1996, which allowed farmers to spray fields after crops emerged. Farmers also use glyphosate before planting to clear weeds and, in some crops and regions, shortly before harvest to dry down crops. This scale of use, making it the most widely used herbicide in the world, explains why questions about its safety, and about the integrity of the research behind it, carry such high stakes for agriculture, public health, and the companies that sell it.

A Familiar Pattern in Other Industries

The Monsanto Papers are not unique. Historians and researchers have documented similar patterns in other industries, in which companies funded research, shaped scientific reviews, or emphasized uncertainty to delay regulation. Internal tobacco industry documents released through litigation in the 1990s revealed decades of efforts to cast doubt on the health effects of smoking. Historians have described how the sugar industry funded research in the 1960s that shifted attention toward dietary fat as the main cause of heart disease. Litigation and investigations have also revealed internal knowledge of health risks in industries producing leaded gasoline, asbestos, and certain PFAS chemicals.

These cases do not prove that every industry-funded study is biased; much industry research is rigorous and necessary. They do show why independence, transparency, and disclosure are essential safeguards, and why internal documents revealed in litigation have repeatedly changed public understanding of corporate science.

Reforms Proposed After the Monsanto Papers

The controversy prompted proposals to strengthen the integrity of chemical regulation. Some of the most commonly discussed include:

Public access to study data. Making the full data from regulatory studies available for independent analysis, as the EU’s transparency regulation now largely requires.

Registration of studies in advance. Requiring companies to notify regulators of studies before they begin, so that unfavorable results cannot be withheld.

Independent testing. Having studies commissioned and overseen by regulators or independent bodies, while still funded by industry fees, to separate funding from control.

Stronger conflict-of-interest rules. Tightening disclosure requirements for journal authors and for scientists serving on regulatory advisory panels.

Journal policies on ghostwriting. Requiring detailed contribution statements and acting promptly when undisclosed involvement comes to light.

Critics of some proposals warn that they could slow regulatory decisions or discourage participation by experts with industry experience. The balance between independence and expertise remains debated.

What It Means for Farmers and Consumers

For farmers who rely on glyphosate, the controversy has created uncertainty about future restrictions and liability, even as regulators in the United States and Europe continue to allow its use. Some have shifted to integrated weed management that reduces reliance on any single herbicide, partly because of glyphosate-resistant weeds. For consumers, the practical guidance remains similar to that for any pesticide: dietary exposure is generally low, washing produce and choosing organic foods reduces residues, and people who apply glyphosate should follow label directions and use protective equipment. The documents themselves are best understood as evidence about how scientific information was produced and presented, a reason for vigilance about research integrity across all regulated products.

Lessons for Scientific Integrity

Whatever one concludes about glyphosate, the Monsanto Papers illustrate problems that extend well beyond one company or one chemical.

Authorship should reflect who did the work. Medical and scientific journals generally require that everyone who made substantial contributions be credited or acknowledged and that funding and competing interests be disclosed. Ghostwriting violates those principles because readers cannot judge potential bias.

Disclosure is necessary but not sufficient. Industry-funded research is not automatically wrong, and much of it is rigorous. But readers and regulators need to know who funded and shaped a study to weigh it appropriately.

Access to data builds trust. When underlying studies are available for independent scrutiny, as EU rules now require for many submissions, it becomes harder for selective summaries to dominate.

Corrections take time. The Williams review was retracted 25 years after publication and eight years after the documents became public, and the decision remains disputed. Scientific self-correction works, but slowly.

How to Read Industry-Linked Research

For readers trying to make sense of competing claims about chemicals and health, a few habits help. Check the funding and conflict-of-interest statements in any study or review. Look for whether a review explains how it selected studies and whether it includes published independent research as well as company data. Give more weight to findings replicated by independent groups. Compare conclusions across organizations with different perspectives, such as regulators, independent cancer agencies, and academic reviews. And be wary of claims, from any side, that a single document settles a complex scientific question.

Why Internal Documents Matter in Science Disputes

Scientific debates usually unfold through published studies, reviews, and regulatory reports. Internal documents add a different kind of evidence: they show how participants behaved behind the scenes, what they knew, and how they tried to shape the public record. Such documents rarely answer the underlying scientific question directly, but they can reveal whether the processes producing scientific consensus were sound.

That distinction is important for interpreting the Monsanto Papers. A ghostwritten review may still summarize data accurately, or it may selectively present evidence; the only way to know is to examine the data independently. Conversely, a substance can be safe even if a company behaved badly in defending it, or harmful even if a company acted in good faith. The documents strengthen the case for independent, transparent evaluation of glyphosate and other chemicals, which is ultimately the best way to answer the scientific question on its merits.

Questions That Remain

Several questions remain open after the retraction. Will regulators formally reassess whether their past evaluations relied on the retracted review, and if so, how? Will the publisher’s investigation of other glyphosate papers lead to further corrections or retractions? Will the EPA’s ongoing registration review incorporate new epidemiological studies and the debate over formulated products versus glyphosate alone? And will reforms to improve transparency in U.S. pesticide regulation gain traction? The answers will shape not only glyphosate’s future but also public confidence in how chemical safety is assessed.

Glyphosate Rules Around the World

Regulatory decisions on glyphosate vary internationally. The European Union renewed glyphosate’s approval in 2023 for ten years, with conditions, after its food safety and chemicals agencies concluded it did not meet the criteria for classification as a carcinogen; several member states have restricted non-agricultural uses such as in parks and home gardens. A few countries have gone further: Vietnam banned glyphosate imports in 2019, and some other governments have announced bans or phase-outs and later delayed or modified them in response to agricultural concerns. In many countries, local governments have restricted its use in public spaces.

These differing decisions reflect differences in regulatory philosophy, political pressure, and how authorities weigh the IARC classification against regulatory risk assessments, rather than fundamentally different scientific data.

How to Explore the Documents Yourself

Many of the internal documents discussed in this article are publicly available through archives maintained by advocacy organizations and in court records from the Roundup litigation. When reading them, it helps to keep a few points in mind. Emails capture fragments of conversations and may lack context, so reading the full thread and related documents matters. Statements by individual employees do not necessarily reflect company policy. Both plaintiffs’ lawyers and the company have strong interests in how the documents are interpreted. Reading independent journalism and academic analyses alongside the documents provides a more balanced picture than relying on excerpts shared on social media.

Key Terms

Monsanto Papers: Internal Monsanto documents made public through Roundup litigation beginning in 2017.

Ghostwriting: Writing or substantially shaping a publication without being credited as an author, usually without disclosure.

Retraction: A journal’s formal withdrawal of a published paper, indicating it should no longer be relied upon.

IARC: The International Agency for Research on Cancer, part of the World Health Organization, which classifies agents by strength of evidence for carcinogenicity.

Good Laboratory Practice (GLP): Standards governing how regulatory safety studies are conducted, documented, and audited.

Preemption: The legal principle that federal law can override conflicting state law.

How Journals Handle Undisclosed Industry Involvement

Most scientific journals now require authors to disclose funding sources, competing interests, and the contributions of everyone involved in a paper, including professional medical writers. Many follow guidelines from the International Committee of Medical Journal Editors and the Committee on Publication Ethics. When undisclosed involvement comes to light, journals can respond in several ways: publishing a correction that adds missing disclosures, issuing an expression of concern while investigating, or retracting the paper if the problems undermine confidence in its conclusions.

In the glyphosate case, three other papers on which Williams was an author received an expression of concern and lengthy corrections in 2018 for incomplete disclosure of ties to Monsanto, according to Retraction Watch. The 2000 review was ultimately retracted rather than corrected because the journal concluded that its conclusions relied solely on unpublished company studies and that its integrity was undermined. Readers can check a paper’s status on the journal’s website or in databases such as PubMed, which flag retractions and corrections.

The Bottom Line

The Monsanto Papers documented real problems in how scientific information about glyphosate was produced and presented, including undisclosed company involvement in a review that shaped perceptions of the herbicide’s safety for a quarter century. The 2025 retraction of that review is a significant correction to the scientific record. But the documents and the retraction do not, on their own, establish that glyphosate causes cancer; that question depends on the full body of toxicological and epidemiological evidence, which scientific bodies continue to interpret differently. The strongest lesson is about process: transparency, independent review, and honest disclosure are what allow the public to trust conclusions about chemical safety, whatever those conclusions turn out to be.

Frequently Asked Questions

What are the Monsanto Papers?

Internal Monsanto documents, including emails and memos, released through U.S. litigation over Roundup beginning in 2017. They addressed ghostwriting of scientific articles, strategies regarding the 2015 IARC classification, and communications with regulators.

Did Monsanto know glyphosate causes cancer?

The documents show the company worked to shape scientific and regulatory debates, and an EPA panel briefly classified glyphosate as a possible carcinogen in 1985 based on contested mouse data before reclassifying it in 1991. They do not establish that glyphosate causes cancer, which remains scientifically disputed.

Why was the 2000 glyphosate review retracted?

In late 2025, Regulatory Toxicology and Pharmacology retracted the Williams, Kroes, and Munro review, citing undisclosed Monsanto involvement in writing it and conclusions on cancer based solely on unpublished company studies.

Does the retraction change glyphosate’s regulatory status?

Not directly. Regulators base decisions on many studies. Critics argue the retraction should prompt re-examination of how regulators weigh industry-controlled evidence.

Is glyphosate still sold?

Yes, glyphosate remains registered and widely used in agriculture. Bayer stopped selling glyphosate-based Roundup to U.S. residential lawn and garden consumers in 2023, replacing it with other active ingredients for that market.

References

1. U.S. Right to Know. Monsanto Papers. usrtk.org
2. Retraction Watch. Glyphosate safety article retracted eight years after Monsanto ghostwriting revealed in court. December 4, 2025. retractionwatch.com
3. Retraction Watch. Publisher investigating two more papers on glyphosate safety over ghostwriting claims. June 15, 2026. retractionwatch.com
4. Williams GM, Kroes R, Munro IC. Retraction notice to “Safety evaluation and risk assessment of the herbicide Roundup and its active ingredient, glyphosate, for humans.” Regulatory Toxicology and Pharmacology. 2025. PMID 41428335
5. The New Lede. Citing “serious ethical concerns,” journal retracts key Monsanto Roundup safety study. December 2025. thenewlede.org
6. ScienceAlert. Retracted: The Monsanto-backed paper that told us Roundup was safe. sciencealert.com
7. Guyton KZ, Loomis D, Grosse Y, et al. Carcinogenicity of tetrachlorvinphos, parathion, malathion, diazinon, and glyphosate. Lancet Oncology. 2015;16(5):490–491. PMID 25801782
8. Andreotti G, Koutros S, Hofmann JN, et al. Glyphosate Use and Cancer Incidence in the Agricultural Health Study. JNCI. 2018;110(5):509–516. PMID 29136183
9. Zhang L, Rana I, Shaffer RM, et al. Exposure to glyphosate-based herbicides and risk for non-Hodgkin lymphoma. Mutation Research. 2019;781:186–206. PMID 31342895
10. U.S. Environmental Protection Agency. Glyphosate. epa.gov
11. Regulation (EU) 2019/1381 on the transparency and sustainability of the EU risk assessment in the food chain. eur-lex.europa.eu

Last updated: October 1, 2026