Glyphosate causes cancer? – large scientific study says no

One of the tropes of the pseudoscience world is that glyphosate causes cancer – but what does real science say? Well, numerous large epidemiological studies have yet to provide evidence of a link that would convince us that the herbicide has any link to any cancer.

Recently, another article in a prestigious cancer journal looked at thousands of  individuals exposed to glyphosate, and once again, have found no convincing evidence that glyphosate causes cancer. The totality of evidence, unless you are into glyphosate- and GMO-free cherry picking, continues to lead us to a simple conclusion – there is no link between the chemical and any of the 200 or more types of cancer.

One of the major issues with the tropes and myths about glyphosate is that many anti-science liberals tend to conflate glyphosate with genetically modified crops. This leads to a lot of unsupported hatred of GMO plants, despite the overwhelming scientific consensus that says that GMO agriculture is safe for humans, animals, and the environment – a consensus as broad and powerful as the one that states that climate change is caused by humans.

So let’s look at this new article, and how it fits into the narrative about glyphosate and cancer.

What is glyphosate?

Glyphosate (Monsanto’s Roundup)  is a broad-spectrum systemic herbicide used to kill weeds, especially annual broadleaf weeds and grasses that are known to compete with commercial crops grown around the world. It has several advantages over many herbicides in that it breaks down in the soil into non-toxic organic molecules, reducing or eliminating contamination of groundwater and lower soils. This is a large improvement over other types of herbicides.

Monsanto has developed genetically modified (GMO) grains that are resistant to glyphosate, so that farms can apply the herbicide to kill the competitive weeds while not harming the crop. This allows farmers to suppress the weeds while allowing better production out of the grain crop. There is robust evidence that glyphosate has no effect on crop yield, while reducing pests at a lower cost than other modalities.

Whatever the benefits of Monsanto glyphosate, GMOs and the herbicide are tied together in many minds. And there is a “chemophobia” amongst many people that all chemicals are bad. But as I discussed before, dose makes the poison – that is, in the real study of toxicology, there are doses of any “chemical” that are safe or unsafe. Water, for example, can be toxic if consumed at certain doses – sure, the dose is high for water toxicity, but it exists. Our culture’s chemophobia makes no sense to people, like me, who understand chemicals – every single thing we consume is made of evil chemicals, some with complex and indecipherable names.

Of course, as a result of this chemophobia, and misinterpreted scientific research, there has been an ongoing effort by many people to claim that glyphosate causes cancer. This, of course, has led to a Monsanto bashing across the internet along with several lawsuits. My article is agnostic about Monsanto – I just don’t care one way or another. All I care about is the quality of evidence that either supports, or refutes, the hypothesis that glyphosate causes cancer.

We’ll look at the new study that has been released examining that hypothesis. I guess if you hate Monsanto and RoundUp, you’ll be disappointed with the evidence from real science. But you know what they say – everyone loves science unless it contradicts their beliefs.

Glyphosate causes cancer study

The research, published in the Journal of the National Cancer Institute (JNCI) and written by Gabriella Andreotti et al., represented a large, long-term study on the use of glyphosate by agricultural workers who handle the chemical. The published study included nearly 45,000 workers in Iowa and North Carolina who had licenses to handle glyphosate.

To jump right to the conclusion, Andreotti et al. found no statistically significant link between exposure to the herbicide and cancer. The study found no association between glyphosate “and any solid tumors or lymphoid malignancies overall, including non-Hodgkin Lymphoma . . . and its subtypes.”

However, the study did find “some evidence of increased risk of acute myeloid leukemia . . . among the highest exposed group,” but added that this association was “not statistically significant.”

In other words, after controlling for confounders like smoking, age, sex, obesity, family history of cancer, and other important factors, there was no evidence of a difference in risk of cancer between farm worker who used glyphosate and those who didn’t

The authors concluded that:

In this large, prospective cohort study, no association was apparent between glyphosate and any solid tumors or lymphoid malignancies overall, including NHL and its subtypes. There was some evidence of increased risk of AML among the highest exposed group that requires confirmation.

And because readers of this article will make the claim that I am a “Monsanto shill“, and that this research was unduly influenced by the evil horde at that company, let me quote the “Funding” section of the article:

This work was supported by the Intramural Research Program of the National Institutes of Health, National Cancer Institute, Division of Cancer Epidemiology and Genetics (Z01CP010119), National Institute of Environmental Health Science (NIEHS; Z01ES0490300), the Iowa Cancer Registry (HHSN261201300020I), and Iowa’s Holden Comprehensive Cancer Center (P30CA086862), as well as the NIEHS-funded Environmental Health Sciences Research Center at the University of Iowa (P30ES005605).

It appears that 100% of the funding came from cancer research centers, NIH, and the National Cancer Institute. Monsanto wasn’t involved.

Finally, this study is in line with other large cohort or case control studies. A meta-review (which are considered to be at the pinnacle of the hierarchy of biomedical research), published in Regulatory Toxicology and Pharmacology, came to this conclusion:

Our review found no consistent pattern of positive associations indicating a causal relationship between total cancer (in adults or children) or any site-specific cancer and exposure to glyphosate.

These researchers based their review on 21 cohort and case-controlled studies. This is extremely powerful evidence that glyphosate doesn’t cause cancer and is unrelated to cancer.

Some people believe glyphosate causes cancer

There are some studies (see here and here) that have attempted to show a link that establishes that glyphosate causes cancer, specifically Non-Hodgkin Lymphoma (NHL). However these type of studies did not tease out glyphosate data from the confounding variables of numerous other pesticides. There are no disagreements that some pesticides cause some types of cancer, so these studies don’t allow us to determine the actual causal factors.

There are also two small studies (here and here), n=4 and 12, respectively, attempted to show a link between glyphosate and NHL. However, they were considered to be essentially case studies which are lower quality types of research because of the small sample sizes.

Once again, the largest studies, of the highest statistical power, show no link between glyphosate and cancer.

Many individuals refer to International Agency for Research on Cancer (IARC), an intergovernmental agency within the World Health Organization and one of the widely respected research groups for cancer causes, statements on glyphosate and cancer:

There was limited evidence in humans for the carcinogenicity of glyphosate. Case-control studies of occupational exposure in the USA, Canada, and Sweden reported increased risks for non-Hodgkin lymphoma that persisted after adjustment for other pesticides.

The AHS cohort did not show a significantly increased risk of non-Hodgkin lymphoma. In male CD-1 mice, glyphosate induced a positive trend in the incidence of a rare tumour, renal tubule carcinoma.

A second study reported a positive trend for haemangiosarcoma in male mice. Glyphosate increased pancreatic islet-cell adenoma in male rats in two studies. A glyphosate formulation promoted skin tumours in an initiation-promotion study in mice. Glyphosate has been detected in the blood and urine of agricultural workers, indicating absorption.

Glyphosate and glyphosate formulations induced DNA and chromosomal damage in mammals, and in human and animal cells in vitro. One study reported increases in blood markers of chromosomal damage (micronuclei) in residents of several communities after spraying of glyphosate formulations.

The Working Group classified glyphosate as “probably carcinogenic to humans” (Group 2A).

I did an extensive critique of the conclusions of the IARC where I  examined several points about their review:

  1. A lot of their research is based on evidence that shows glyphosate is in the blood and urine of farmworkers. These results do not show any causal link to anything, especially cancer. It has been established that farmworkers who use a lot of glyphosate may show higher blood levels of the chemical. But that’s a long way to demonstrating that glyphosate causes cancer.
  2. In addition, some of their research is based on animal studies. I am certainly not a fan of animal studies to show anything except some mice and rats might get cancer after consuming rather large quantities of glyphosate. Less than 10% of animal studies ever lead to clinical significance, so making a broad proclamation based on animal studies is not useful.
  3. They seemed to ignore the high quality systematic reviews (again, at the top of the heap of biomedical research) that clearly refute the hypothesis that glyphosate causes cancer.
  4. Finally, the IARC is very conservative in its writing and conclusions. So it may be that they are much more willing to rate a compound as carcinogenic than not, possibly as a result of the precautionary principle.


David Spiegelhalter, a professor at Britain’s Cambridge University and an expert in analyzing statistical risks, who has no link to the research, said the results were from a “large and careful study” and showed “no significant relationship between glyphosate use and any cancer.”

I know, people are going to get mad at these results just because they don’t like them. They want to believe Monsanto is evil (maybe they are, but not because of glyphosate). They want to believe that glyphosate causes cancer, because all chemicals are bad. They want to believe that GMOs are bad because glyphosate.

But once again, these science deniers want to pick and choose the science that meets their preconceived notions. They have a conclusion, glyphosate is bad, and they cherry pick data that supports their conclusion, without ascertaining whether the quality of research performed is good or bad.

The research presented herein, from G Andreotti and many others, is a large, high quality study published in a respected journal, firmly rejects the hypothesis that glyphosate causes cancer. And it is in line with numerous other high quality reviews and research that shows the same.


The Original Skeptical Raptor
Chief Executive Officer at SkepticalRaptor

Lifetime lover of science, especially biomedical research. Spent years in academics, business development, research, and traveling the world shilling for Big Pharma. I love sports, mostly college basketball and football, hockey, and baseball. I enjoy great food and intelligent conversation. And a delicious morning coffee!