Addressing 10 controversial claims on glyphosate weedkiller: Agricultural advances have made farming and our foods safer and more abundant than at any other time in history. Everyone wants safe food and sustainable farming. But modern technologies are victims of their own success, and media ecosystems exacerbate confusion. And while everything is a chemical—and chemicals enable food production—the word evokes fear and anxiety. Well-funded disinformation campaigns exploit this chemophobia to sow fear about the dangers of specific technologies, which undermine consumer confidence in agriculture and our food.
By Andrea Love, Kevin Folta, and Nicole Keller
Few chemicals are more vilified than the herbicide glyphosate (Jun et al. 2023). Glyphosate, the active ingredient in weed control brands such as Roundup, has been used for decades, mostly without controversy (Duke 2018). Many farmers attribute their farms’ survival to glyphosate. Scientific consensus and fifty years of regulatory scrutiny continue to conclude that glyphosate is a relatively benign chemical, safe for use as directed, and poses next-to-no risk to humans (Solomon 2020). Yet media outlets repeat claims that glyphosate causes everything from autism to cancer to bee extinction. Recently, an article in the prominent medical journal Pediatrics recommended that trace dietary exposures should be avoided by children (Abrams et al. 2024).
Why does a disparity exist between evidence and perception and between experts and “experts”? How do we assess the benefits and any potential risks of glyphosate?
What Is Glyphosate?
Glyphosate [N-(phosphonomethyl) glycine] is a nonselective herbicide; in other words, it kills plant species indiscriminately. John Franz, PhD, of the Monsanto Company characterized its herbicidal activity, first on the market as Roundupin 1974. Today, over 750 glyphosate formulations for weed control are produced by numerous companies globally.
Glyphosate kills plants by interfering with 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), an enzyme essential for production of key amino acids (Duke 2018). Without these amino acids, proteins cannot be synthesized, and the plant dies. All plants have this biochemical pathway, explaining glyphosate’s broad toxicity in plants. Glyphosate has no direct pharmacological effects on animals (including humans), which lack this enzyme. Dozens of international regulatory bodies have therefore recognized glyphosate as a low-toxicity chemical with infinitesimal risk to animals at levels encountered (Genetic Literacy Project 2023).
Why was glyphosate widely adopted? Historically, farmers would plant a field of seeds and used cultivation or other herbicides to control weeds. Soil disruption caused topsoil loss from wind and rain and required labor, fuel, and time. Weed control practices radically changed when scientists invented glyphosate-tolerant (GT) crops—available for public use in 1996. Scientists identified a bacterial EPSPS variant that was not impacted by glyphosate (“glyphosate tolerant” or GT) and transferred this GT-enzyme into corn, soybeans, sugar beets, canola, and alfalfa. These plants then possessed EPSPS unaffected by glyphosate, so weed control could be accomplished with this singular herbicide (Duke and Powles 2008).
Ease of use, broad spectrum weed control, low cost, minimal environmental impacts, and limited risk to applicators made glyphosate an obvious choice to protect crops from weeds that compete for soil resources.
Legitimate Glyphosate Risks
While glyphosate has low acute toxicity to nontarget organisms, like with anything, risks can exist at excessive exposures. The 50 percent lethal dose is less than 5,000 mg/kg body weight (Turkmen and Dogan 2020), meaning a 220-pound person would have to consume less than 500 grams of pure glyphosate to reach that. While rare reports of self-harm from intentional ingestion of glyphosate exist (Lee et al. 2000), it remains an uncommon cause of human toxicity, certainly not via food or farming exposures.
A primary environmental concern is the emergence of glyphosate-tolerant weeds (Perotti et al. 2020). Much like antibiotic overuse selecting for bacteria able to survive those chemicals, weed species have similarly adapted. Over forty-eight weed species have developed mechanisms to survive in the presence of glyphosate since use on genetically engineered crops began in 1996 (Baek et al. 2021). This required companies that produce GT seeds to incorporate additional herbicides in crop management, not ideal when these technologies aim to minimize herbicide use and environmental impact.
Concerns about glyphosate-based herbicide use around aquatic environments are irrespective of glyphosate itself (Tresnakova et al. 2021). Herbicides are applied with a surfactant, a soapy chemical that improves plant tissue penetration. Surfactants break surface tension of water and can themselves pose a risk to microbial communities, insects, and even fish in aquatic ecosystems (Annett et al. 2014; Relyea 2018). Because nontarget plants such as duckweed and other sentinel species may be impacted, glyphosate is restricted around water environments.
When used appropriately with real-world doses, glyphosate poses little risk to the applicator, consumer, or environment as has been demonstrated with over fifty years of use on farm and residential applications.
Glyphosate Exposure in Humans
Human exposure to glyphosate is physiologically insignificant. Claims that insinuate human risk from glyphosate are based on infinitesimal levels detected on foods or in urine (Zoller et al. 2020). This underscores a fundamental challenge when discussing pesticides: detection doesn’t equal harm. Every chemical has a toxicity threshold dependent on dose. Pesticides might be detected in food at levels measurable only by the most sensitive analytical chemistry tools. We can detect levels of substances that are irrelevant to our health, measures in parts per billion or parts per trillion. A part per billion (ppb) equals fifty drops of water in an Olympic-sized swimming pool, or one second of time in 31.7 years. A part per trillion (ppt) equals one drop of water in twenty Olympic-size swimming pools, or one second of time in 31,700 years.
Glyphosate exposure levels (maximum residue limits, or MRLs) are set and routinely reevaluated by international agencies to ensure farmer compliance and minimal exposure. For added safety, MRLs are set orders of magnitude below levels that would pose theoretical risks to consumers and account for sensitive populations—children, pregnant women, and those with higher exposure (e.g., farmers) (Winter 2015). The MRL for glyphosate varies by the crop, but ranges from 0.1 to 400 parts per million (ppm) per day (Vicini et al. 2021). Detected levels routinely cited in anti-glyphosate campaigns are far lower than these MRL values.
What levels are humans actually exposed to? The water solubility of glyphosate ensures it is rapidly excreted in urine and stool, making exposure analysis simple. A commonly cited paper in opposition to glyphosate found median glyphosate levels in urine are not only miniscule but nearly identical between people who consume conventional or organic food, 390 ppt versus 400 ppt, respectively (Ospina et al. 2022). A review of the literature reports urine levels ranging from 260 ppt to 73.5 ppb (Gillezeau et al. 2019). For reference, 400 ppm, the highest MRL level of glyphosate, is equal to 40,000 ppb or 400,000,000 ppt.Levels detected in urine are up to a million times lower than the already conservative maximum residue limits, confirming dietary exposure does not pose even a theoretical health risk.
Sensational Unsupported Claims
Glyphosate remains a staple on many farms, so media outlets, activist groups, and even some scientific journals continue to allude to the dangers of crops “doused in Roundup.” In 2012, a credible scientific journal published a paper by G.E. Seralini and coauthors demonstrating that rats fed glyphosate developed tumors. Deeper inspection revealed the authors used a statistically small number of a strain of rats prone to tumor growth, and control rats also developed tumors (Arjó et al. 2013; Sánchez and Parrott 2017). The paper was retracted by the journal, then later appeared in a new journal without changes or additional review in 2014. The European Union sponsored three independent follow-up studies that failed to replicate the original claim (Steinberg et al. 2019; Zeljenková et al. 2016; Coumoul et al. 2019).
Around the same time, an “independent researcher” and an MIT researcher in artificial intelligence published several reviews in low-quality journals with no original research. The reviews contain an incredible cherry-picking and citation bias, selectively using slivers of data from original research that supports the authors’ narrative. One paper, “Glyphosate, Pathways to Modern Diseases II” (Samsel and Seneff 2013) and “Glyphosate, Pathways to Modern Diseases III” (Samsel and Seneff 2015a) suggested glyphosate is the cornerstone of gluten intolerance, infertility, miscarriages, birth defects, kidney failure, cancer, and a spate of other disorders. These claims arise from misinterpretation of correlative data related to glyphosate use and Parkinson’s disease, thyroid cancer, and end-stage renal disease. In a subsequent review, they link glyphosate to autism, chronic fatigue, depression, Parkinson’s disease, and prion disease (Samsel and Seneff 2015b). They posit glyphosate is in vaccines and underlies an increase in autism (Beecham and Seneff 2016), claiming that glyphosate exposure will cause 50 percent of children to be autistic by 2025 (Faria 2015).
The origin of the glyphosate in vaccines claim was Moms Across America, an organic food activist group with a history of publishing false or doctored information. A nonpeer-reviewed online newsletter shows they contracted a laboratory to perform measurements and claimed to have detected glyphosate in vaccines (Honeycutt 2016). They amplified claims made by U.S. Public Interest Research Group (PIRG) that glyphosate was in wine, beer (Cook and U.S. PIRG Education Fund 2019) and breast milk (Honeycutt 2014). The problem? The commercial kit used is extremely sensitive but validated for use only with water and urine. Breast milk, vaccines, wine, and beer are complex solutions containing countless molecules that could elicit false positive results. Properly executed follow-up work on breast milk failed to detect glyphosate (McGuire et al. 2016; Steinborn et al. 2016), and 95 percent of wine samples contained less than 5 ppb glyphosate (Pérez-Mayán et al. 2022). Glyphosate is used to control weeds in vineyards, but not applied to grapes or grapevines.
Glyphosate was also implicated in chronic kidney disease of unknown origin (CKDu) based on correlations (Ulrich et al. 2023). Glyphosate is used to control weeds on tea plantations in Sri Lanka. When farm workers started presenting with an unusual kidney disorder, an investigating medical researcher mentioned glyphosate as a hypothetical cause in a review article (Jayasumana et al. 2014). Social media instantly transformed this guess into gospel, despite no causal evidence of it causing kidney disease. This led to a glyphosate ban in Sri Lanka, increasing production costs for farmers and contributing to food shortages (Marambe and Herath 2020; Dorlach and Gunasekara 2023).
A July 2022 report insinuated that glyphosate causes Alzheimer’s disease. The claim exaggerated preclinical research assessing glyphosate in rodents (Winstone et al. 2022). The authors demonstrated that glyphosate consumed by mice was detectable in the brain and corresponded with increased expression of neural inflammation biomarkers. The university communications group wildly extrapolated that to insinuate a link with Alzheimer’s disease, which anti-biotechnology groups were quick to amplify. Public communications neglected to mention the mice were fed massive doses of glyphosate daily for two weeks before the assessment, levels that could never be encountered without chugging glyphosate.
These are a sample of how, by accident or design, peer-reviewed literature appears to validate unfounded risks associated with glyphosate. Legitimate findings were exaggerated to alarming absurdity by clickbait headlines and class-action attorneys ready to cash in on a manufactured crisis. There are several individuals with academic credentials misinforming conferences and publishing unsubstantiated associations between glyphosate and every disease or disorder that plagues us. It is these sensational stories that skew public perception, cause health anxiety, and create a disinformation landscape around one of agriculture’s safest chemistries.
Cancer and the IARC Classification
Activists opposed to biotech crops switched their focus from the crops to the chemistries used on them—and glyphosate was the perfect villain. As acres of glyphosate tolerant crops expanded, so did the use of glyphosate, making it easy to hint at correlations between the disease-of-the-day and increased glyphosate use.
This controversy was borne out of slight, statistically nonsignificant associations between certain cancers in farmers that used glyphosate and some in vitro and animal studies. This was enough for the International Agency for Research on Cancer (IARC), a working group of the World Health Organization (WHO), to label glyphosate as a “probable” carcinogen in 2015. This ignited a firestorm of litigation against Bayer, one of many glyphosate manufacturers. Juries, swayed by emotions and legal narratives instead of science, ruled in defense of plaintiff’s cases—reinforcing false associations to cancer and making it more challenging for credible science to prevail in public discussion.
The issue with a “probable carcinogen” classification? The IARC does not assess risk, only hazards. This means the question IARC is asking is “Could glyphosate theoretically cause cancer under any circumstance?” and not “Is there evidence of a realistic likelihood that glyphosate causes cancer based on exposures humans may encounter?” IARC even conceded that there is “no known link between dietary glyphosate exposure and cancer.” Leaked drafts indicated IARC excluded robust human data that showed no link between glyphosate and cancer, while relying on weak observational studies, animal, and in vitro data.
The IARC report augmented deep divisions between scientific and agricultural communities and the public, exacerbated by additional flawed reports shared widely. One meta-analysis exploded across the internet, claiming a 41 percent increase in non-Hodgkin’s lymphoma in exposed groups (Zhang et al. 2019). However, critics noted the curious grouping of data that led to positive associations (Kabat et al. 2021), and parallel analyses showed no association (Donato et al. 2020). Even a decade after the IARC classification, there is thin epidemiological or mechanistic evidence to support a relationship between glyphosate exposure and any human cancers.
International regulatory bodies that do assess risk and included robust epidemiological studies in their assessment have independently concluded there is no relationship between glyphosate and cancer. These include the Joint FAO/WHO Meeting on Pesticide Residues (JMPR; Food & Agriculture/World Health Organization), the U.S. Environmental Protection Agency (EPA), The National Academies of Sciences (NAS), the European Food Safety Authority (EFSA), the European Chemicals Agency, and Health Canada. All evaluated hundreds of studies across decades of data and concluded there is no solid evidence of glyphosate causing cancer in humans. EFSA rebuked the IARC classification as inappropriate based on data. The European Commission reapproved glyphosate for use for another ten years in 2023.
A Toolkit for 10 Common Claims about Glyphosate
A well-funded and motivated disinformation enterprise bombards social media with glyphosate claims. Here are rebuttals:
1. “Its use has increased massively.” It is true; the raw kilograms of herbicide applied internationally have increased significantly since 1996. Before 1996, it was used as a general herbicide. After 1996, it was used to weed massive expanding acreage of genetically engineered crops. But it replaced other herbicides that carried more risk to humans and environment (Duke et al. 2012), meaning a net gain in safety and environmental stewardship.
2. “It has been ‘detected’ in [insert food, drink, or body fluid here].” Modern analytical chemistry is incredibly sensitive and allows glyphosate to be detected down to the parts per trillion (one second in 31,700 years). Detection does not equal risk; with everything, the dose makes the poison.
3. “Crops are doused in glyphosate.” Farmers apply about 750 ml of active ingredient per acre early in plant development. That’s roughly two soda cans per football field. Not only are crops not “doused,” the herbicide is sprayed on herbicide-tolerant plants long before the corn, soybeans, or canola seeds are on the plant.
4. “It caused [problem x] in rats.” There are animal studies that show evidence of harm. However, these studies typically administer massive amounts over long periods of time, and rodents have very different physiologies than humans. Be sure to check the dose and research model when vetting claims.
5. “It causes cancer.” There has never been definitive, reproducible data suggesting any link to human cancers. The IARC categorization of “probable carcinogen” is a hazard assessment based on a small number of suggestive animal and petri dish studies. In the almost ten years since the IARC reclassification, there is no sound epidemiological or mechanistic evidence of causality.
6. “It is linked to [insert disease, disorder, or condition here].” Claims that it is “linked” to cancer, autism, etc., should raise skeptical red flags. In this context, a “link” can be a one-off paper, retracted study, weak statistical blip, or rangy correlation. A link does not mean actual risk. Many anti-glyphosate organizations will show correlations between a given disease and use of the herbicide in total kilograms. Correlation does not equate to causation. It is important to note that in fifty years of use, research, and international regulatory scrutiny, no disease has been shown to be causally associated with occupational or dietary exposure.
7. “It causes digestive problems when sprayed to dry wheat.” Occasionally, grain crops are treated with glyphosate to ensure the product, typically wheat, dries uniformly. Claims that this causes gluten sensitivity, “leaky gut,” and other nebulous medical conditions are unfounded. Glyphosate does not “alter” gluten structure as is sometimes claimed, and levels of glyphosate found on wheat products are too low to even hypothetically cause these issues.
8. “It destroys the microbiome.” In vitro experiments and in silico projections suggest that glyphosate might inhibit favorable bacteria while elevating harmful bacteria in the intestine. Aside from the fact that in vitro studies cannot recapitulate the complexity of the human digestive system, trace levels of glyphosate consumed through food are too low to cause these issues, especially because bacteria do not take up glyphosate well without additional surfactants.
9. “It is killing bees.” Bees visit flowers. Plants sprayed with glyphosate either do not flower or flowers rapidly die. The exceptions are genetically engineered crops such as canola that flower and attract bees. However, residues present in nectaries and pollen range from “below detection” to 205 ppb, a level unlikely to cause harm, and is undetectable two months following application (Zioga et al. 2022). Bees fed higher chronic exposures in the laboratory at 2.5 ppm have shown some effects on foraging behaviors (Farina et al. 2019). Others fed 5–10 ppm in sugar water for five days showed negative effects on microbiome composition (Motta et al. 2018). High concentrations used were designed to mimic those in recent applications (Motta and Moran 2023), so data must be considered with that caveat.
10. “Look at the lawsuits: RoundUp causes cancer.” Monsanto (now Bayer) has both lost and won court cases. Lawsuits and jury trials are not scientific evidence of health effects, merely evidence that a jury was persuaded by a convincing (i.e., emotional) appeal. Anyone can sue anyone for anything, and juries are not inherently scientific experts. This is a red herring that ignores fifty years of scientific evidence.
Conclusions
Modern agriculture seeks to fill gaps in food security, reinforcing and improving human health. A new eye on sustainability welcomes new (and occasionally old) technology to make land use more efficient and lessen environmental impact. With intrinsic concerns of health, safety, environmental stewardship, and farmers’ economic sustainability, glyphosate has met these goals for five decades. While there is insufficient evidence of health impacts at current exposures, use has been and will continue to be monitored closely. Ongoing research should continue to be alert for any actual risk, perhaps in certain population segments. As of the writing of this article, glyphosate remains useful for farmers to ensure productivity, affordability, and stability of food crops. Although it remains a political target, our job as a scientific and skeptical community is to continue to evaluate claims for veracity and clearly communicate actual risk and benefits to the public.
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Authors
Kevin Folta, PhD, is a professor, keynote speaker, and host of the Talking Biotech podcast. Follow Professor Folta on X @kevinfolta
Andrea Love, PhD, is a biomedical scientist and award-winning science communicator with a PhD in microbiology and immunology. In addition to her fulltime career in life sciences biotechnology, she is the author of ImmunoLogic and the executive director of the American Lyme Disease Foundation. She can be reached at drandrealove@immunologic.org. Follow Andrea on X @dr_andrealove
Nicole Keller, DO, FAAP, is a general pediatrician practicing in suburban/rural Chicagoland. She serves as chairperson of the pediatric department at the medical center she is a part of. She can be reached at nicole.keller.do@gmail.com.
