Roundup Failure to Warn Claims: What Monsanto Knew and When

You followed the label. You trusted that a product sold in every hardware store was safe for your yard, your job, or your farm. Now you’re facing a non-Hodgkin’s lymphoma diagnosis from Roundup use, and you want to know whether anyone told you the whole truth about the risk.

That question sits at the center of Roundup failure to warn claims, the legal theory behind many of the biggest verdicts against Monsanto and its parent company, Bayer. This guide explains what failure to warn means and why it matters for your case.

In this post, you’ll learn:

What “failure to warn” means under product liability law
What internal documents suggest Monsanto knew about glyphosate
How juries and courts have responded to these arguments
How the theory applies if you’ve been diagnosed with non-Hodgkin’s lymphoma

What Does “Failure to Warn” Mean in Product Liability Law?

Manufacturers have a legal duty to warn consumers about known or reasonably knowable dangers in their products. When a company fails to provide adequate warnings or instructions, and someone gets hurt as a result, the company can be held liable. This is true even if the product was made exactly as designed.

In California, a failure to warn claim can be brought under two main theories:

Strict liability failure to warn. The plaintiff must show the risk was known or knowable based on the scientific knowledge available at the time. The company can be liable even if it did not act carelessly.
Negligent failure to warn. The plaintiff must show the company knew or should have known of the danger and acted unreasonably by not warning users.

What Makes a Warning “Adequate”?

A warning isn’t adequate just because it exists. It must clearly describe the specific risk, reach the people who use the product, and give them enough information to protect themselves. A label that covers eye irritation but says nothing about cancer does not warn users about cancer.

This matters because a proper warning changes behavior. People who know about a cancer risk may wear gloves and masks, wash their clothes separately, or choose another product entirely.

How Failure to Warn Applies to Roundup

Roundup’s active ingredient, glyphosate, is the most widely used herbicide in the world. For decades, Monsanto marketed Roundup as safe for people and pets when used as directed. Its label has never included a cancer warning.

The legal turning point came in 2015. That year, the International Agency for Research on Cancer, part of the World Health Organization, classified glyphosate as “probably carcinogenic to humans.” It noted a link to non-Hodgkin’s lymphoma. In 2017, California added glyphosate to its Proposition 65 list of chemicals known to the state to cause cancer.

Plaintiffs argue Monsanto had reason to know about the risk long before 2015. The claim is not only that the company failed to add a warning. It is that the company actively worked to shape the science and public opinion so that no warning would seem necessary.

What Internal Documents Revealed About Monsanto’s Knowledge

Much of the evidence in Roundup trials comes from Monsanto’s own files. Internal emails, memos, and reports released during litigation became widely known as the “Monsanto Papers.” Plaintiffs’ attorneys have used these records to show juries what the company knew and how it responded.

Concerns About the Formulated Product

Roundup is not pure glyphosate. It is a formulated product that includes surfactants, which help the chemical penetrate plant surfaces. Plaintiffs have argued that the combination may be more toxic than glyphosate alone.

One internal Monsanto email, often cited at trial, stated that the company could not say Roundup does not cause cancer because it had not done the necessary testing on the formulation. Juries have heard this as an admission that key safety questions were never answered.

Ignored Calls for Further Testing

Evidence presented at trial showed that in 1999, an outside scientist Monsanto hired reviewed glyphosate’s potential to damage genetic material. He recommended additional testing. Plaintiffs have argued the company did not follow through and instead looked for other experts whose views were more favorable.

Allegations of Ghostwritten Research

Internal emails suggested Monsanto employees helped draft scientific papers that were later published under the names of outside researchers. Plaintiffs claim these papers were used to reassure regulators and the public that glyphosate was safe. Monsanto has denied wrongdoing, but jurors in several trials found this evidence persuasive.

Efforts to Undermine Cancer Findings

Documents also showed the company planned a strategy to challenge the IARC classification before it was even announced. For plaintiffs, this pattern matters. It suggests the company’s focus was protecting its product, not informing the people who used it.

How Courts and Juries Have Responded

Juries have repeatedly found Monsanto liable on failure to warn grounds. While some awards have been reduced on appeal, the verdicts show how seriously jurors take the company’s conduct.

Notable Roundup Verdicts

Johnson v. Monsanto (2018): A San Francisco jury awarded a school groundskeeper $289 million after finding Monsanto failed to warn of Roundup’s cancer risk. The award was later reduced to about $78 million.
Hardeman v. Monsanto (2019): A federal jury in San Francisco awarded $80 million, later reduced to about $25 million. A federal appeals court upheld the verdict in 2021.
Pilliod v. Monsanto (2019): An Alameda County jury awarded a married couple more than $2 billion. The award was later reduced to about $87 million.
Barnes (2025): A Georgia jury returned a verdict of more than $2 billion for a man who linked his non-Hodgkin’s lymphoma to Roundup.

Many of these awards included punitive damages. Juries award punitive damages to punish conduct they find especially harmful, such as concealing known risks. Bayer has also won a number of trials, which is why every case depends on strong evidence and preparation.

The Scale of the Litigation

Bayer acquired Monsanto in 2018 and inherited its Roundup liability. In 2020, it announced a settlement program worth roughly $10.9 billion. The company has faced more than 177,000 Roundup-related claims and has set aside nearly $16 billion to resolve them.

The Federal Preemption Defense

Bayer’s main legal defense is federal preemption. The company argues that because the EPA approved Roundup’s label without a cancer warning, federal law bars state failure to warn claims. Put simply, Bayer says it could not have added a warning the EPA didn’t require.

Courts have split on this issue. Several federal appeals courts, including the Ninth Circuit covering California, rejected Bayer’s argument, while the Third Circuit sided with the company. The question has now reached the U.S. Supreme Court in Monsanto v. Durnell. Because this area of law continues to develop, an attorney can explain how the latest rulings may affect your claim.

Why Failure to Warn Is the Backbone of Roundup Lawsuits

Roundup lawsuits often include several legal theories, such as design defect and negligence. Failure to warn tends to carry the most weight for three main reasons.

It tells a clear story. Jurors understand the idea that a company should tell people about serious risks. The question “What did they know, and why didn’t they tell you?” resonates in the courtroom.

The evidence is strong. Monsanto’s own documents give plaintiffs direct proof of the company’s knowledge and decisions. That’s more compelling than expert opinion alone.

It supports punitive damages. When evidence suggests a company hid known dangers, juries may find malice or fraud. That finding can lead to punitive awards that increase the value of a case and put pressure on the defendant to settle.

How Failure to Warn Applies to Non-Hodgkin’s Lymphoma Plaintiffs

If you’ve been diagnosed with non-Hodgkin’s lymphoma after Roundup exposure, a failure to warn claim may be the strongest path to compensation. Your legal team will need to prove several key elements.

What You Need to Show

Exposure. You used Roundup, or were regularly exposed to it, over a meaningful period of time.
Knowledge of the risk. The cancer risk was known or knowable to Monsanto during the time you were exposed.
An inadequate warning. The Roundup label did not warn you about cancer.
A different choice. A proper warning would have changed your behavior, such as wearing protective gear or avoiding the product.
Causation. Roundup exposure was a substantial factor in causing your non-Hodgkin’s lymphoma.

Common NHL Subtypes in Roundup Cases

Many Roundup plaintiffs have been diagnosed with subtypes such as diffuse large B-cell lymphoma, follicular lymphoma, mantle cell lymphoma, or chronic lymphocytic leukemia/small lymphocytic lymphoma. Your medical records will help establish your diagnosis and rule out other causes.

Evidence That Strengthens Your Claim

Medical records confirming your diagnosis and treatment
Employment records showing work in landscaping, farming, or groundskeeping
Receipts, photos, or witness statements showing home use
A timeline of how often and how long you used Roundup

Don’t Wait Too Long

In California, personal injury claims generally must be filed within two years of when you knew, or reasonably should have known, that your illness was linked to Roundup. Wrongful death claims have similar limits. Evidence is also easier to gather while memories and records are fresh.

Common Mistakes That Can Weaken a Failure to Warn Claim

Protect your case by avoiding these missteps:

Assuming you missed the deadline. The discovery rule may give you more time than you think.
Throwing away old records. Receipts, pay stubs, and photos can prove exposure.
Downplaying your use. Be honest and thorough with your attorney about every source of exposure.
Giving statements to insurers or company representatives. Talk to a lawyer first.

Talk to Walch Law About Your Roundup Claim

Monsanto had a duty to tell you about the risks of its product. If evidence shows it chose not to, the law gives you a way to hold the company accountable. A failure to warn claim can help cover medical bills, lost income, and the pain your family has endured.

Walch Law represents people across Los Angeles and throughout California who developed non-Hodgkin’s lymphoma after Roundup exposure. We handle Roundup cases on a contingency fee basis, so you pay no attorney fees unless we recover compensation for you. Contact Walch Law today for a free, confidential consultation, and let us help you understand your options.

Frequently Asked Questions

What is a Roundup failure to warn claim?
It is a product liability claim alleging Monsanto knew or should have known that Roundup could cause cancer but did not warn users on its label.

Does Roundup’s label include a cancer warning?
No. Roundup’s label has not included a cancer warning, which is a central issue in these lawsuits.

Can I file a claim if I used Roundup at home, not at work?
Yes. Homeowners and gardeners who developed non-Hodgkin’s lymphoma after regular use may have a claim.

What if Bayer wins its preemption argument?
The outcome could affect how failure to warn claims move forward, but other legal theories may still apply. An attorney can explain how current law affects your case.

How much does it cost to hire Walch Law?
Roundup cases are handled on a contingency fee basis. You pay no attorney fees unless your case recovers compensation.