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The Weedkiller Used by Monsanto Does Not Cause Cancer, Long-Term Study Reveals

Misinformation reigns.

10 NOV 2017

A long-term study of Glyphosate from scientists at the National Cancer Institute (NCI) has found no compelling evidence that the controversial weedkiller causes cancer.

Glyphosate, the active ingredient in Roundup, is the most commonly used herbicide worldwide and was first introduced by Monsanto in 1974. The weedkiller is often used with crops that have been genetically modified to resist the herbicide. This allows farmers to kill off weeds without also killing off the crops that they are trying to grow.


The chemical is shrouded in controversy, with many critics arguing that the weedkiller can cause a variety of medical conditions, including autism, gluten allergies, "leaky gut" syndrome and even cancer. Often, these critics point to the elevated cancer rates observed in farmers as evidence of the chemical's dangerous nature.

But correlation and causation are two very different things.

NCI's long-term study looked at nearly 50,000 people who used glyphosate to see if they developed any type of cancer over time. The research relied on data collected for the Agricultural Health Study (AHS), which tracks the health of tens of thousands of agricultural workers, farmers and their families in Iowa and North Carolina.

While there was "some evidence" that linked the weedkiller to acute myeloid leukemia, the link was "not statistically significant." Overall, the report was unable to find a significant association between glyphosate and most cancers.

The study is supported by previous research from the World Health Organization and the Food and Agriculture Organization of the United Nations. These organizations released a joint report in 2016 that found glyphosate poses no cancer risks and does not impact human genetics.


Just last year, one of the most extensive reports on the herbicide was released by the US Environmental Protection Agency (EPA). It found that glyphosate is "'not likely to be carcinogenic to humans' at the doses relevant to human health risk assessment." 

Even still, it is doubtful that these findings will make the controversy go away.

In 2015, a report by the International Agency for Research on Cancer (IARC) ranked glyphosate as a Group 2a carcinogen. At the time, the World Health Organization jumped on the study, and declared glyphosate was "probably carcinogenic" for humans.

The information spread like wildfire, prompting international disputes and multi-million dollar lawsuits. 

But the information was not entirely true.

Last month, it came to light that the results of the IARC's assessment of glyphosate were tampered with. According to journalists at Reuters, statistical analyses were inserted that effectively reversed the original finding of the study being reviewed by the IARC. And - in some instances - information was actually deleted.

For instance, the original report "firmly" and "unanimously" agreed that glyphosate had not caused abnormal growths in the mice being studied. But in the final version, that sentence had disappeared completely.


BEFORE & AFTER: A draft of IARC's assessment of glyphosate (top) cited animal research findings that the compound didn't cause tumours; the published version concluded the opposite.

All in all, Reuters found 10 significant changes that were made between the draft and the final version of the report. In every single one of those ten cases, a negative association between glyphosate and cancer was either deleted or replaced with a neutral or positive one.


Reuters was unable to determine who made the changes, and the IARC would not comment on the findings.

Two years later, this report is still being referenced by anti-GMO and anti-glyphosate critics.

In the same week that the NCI report revealed no association between cancer and glyphosate, the New York Times reported that the European Union has refused to re-authorize the use of glyphosate for another five years.

Despite evidence to the contrary, glyphosate continues to be seen as harmful to public health.

The report was published in the Journal of the National Cancer Institute on Thursday.