Does Glyphosate Cause Cancer? Why The EPA and WHO Reached Opposite Conclusions

Consumer Goods

Over 125,000 lawsuits have been filed against Monsanto because plaintiffs allege that glyphosate, the main active ingredient in the world’s best-selling herbicide, Roundup, caused them to develop cancer. 

In 1985 the U.S. Environmental Protection Agency (EPA) classified glyphosate as a Class C carcinogen, which means there is suggestive evidence of carcinogenic potential. 

Thirty years later, the World Health Organization’s International Agency for Research on Cancer classified glyphosate as “probably carcinogenic to humans.” 

But flashback to 1991, when the EPA did an about-face on glyphosate, reclassifying it from Class C status to Class E, which suggests evidence that a substance is non-carcinogenic to humans. According to an article, “A Short History of Glyphosate” on, this was the same year that the Monsanto Corporation was developing its first generation of Roundup ready GMO crops. 

To date, only three Roundup lawsuits have gone to trial. All three have seen plaintiffs emerge victorious. In the three plaintiff wins, evidence was presented that showed Monsanto went to great lengths to conceal the potential carcinogenic nature of glyphosate. Internal documents reveal that Monsanto placed pressure on the EPA and colluded with the regulatory agency to conceal the dangers of glyphosate. Moreover, the company ghost wrote scientific papers to support the position that glyphosate does not cause cancer. Monsanto successfully pressured the editor of Food and Chemical Toxicology Journal to retract a study, which showed that a strain of Roundup Ready GMO corn causes cancer in rats. lists the other questionable business tactics employed by Monsanto that were uncovered during the Roundup trials. The website also details the lengths to which Monsanto was able to get the Food and Chemical Toxicology Journal study retracted

Setting aside all that, however, what does the actual research say? How can Bayer, which acquired Monsanto in 2018 for $62 billion, say that the research shows that glyphosate is safe while juries in the three court cases against Monsanto reached opposite conclusions? And to pose the question in another way, consider this research article in Environmental Sciences Europe, titled, “How did the US EPA and IARC reach diametrically opposed conclusions on the genotoxicity of glyphosate-based herbicides?”

The article reached three conclusions: 

1) The EPA relied mostly on registrant-commissioned, unpublished regulatory studies, 99% of which were negative, while IARC relied mostly on peer-reviewed studies of which 70% were positive (83 of 118). 

2) EPA’s evaluation was largely based on data from studies on technical glyphosate, whereas IARC’s review placed heavy weight on the results of formulated glyphosate herbicides and a soil metabolite called aminomethylphosphonic acid. 

(3) EPA’s evaluation was focused on typical, general population dietary exposures assuming legal, food-crop uses, and did not take into account, nor address generally higher occupational exposures and risks (to groundskeepers, farmers and gardeners). 

The researchers suggested that instead of relying strictly on the toxicity of glyphosate from eating food, ongoing research “Should be focused on studies relevant to the biological impacts triggered by exposures to widely used, formulated glyphosate-based herbicides.”

Added the researchers, “Much less effort has been invested by EPA in assuring that occupational and worker-risk assessments are based on accurate exposure and toxicological data.” Such scenarios, the researchers said, should include when, where, how, and how frequently and heavily a formulated glyphosate herbicide is applied by a given person.

In summarizing the different conclusions reached by EPA and the WHO’s IARC, the researchers wrote: “IARC’s evaluation relied heavily on studies capable of shedding light on the distribution of real-world exposures and genotoxicity risk in exposed human populations, while EPA’s evaluation placed little or no weight on such evidence.”


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