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"The Weight of Evidence Strongly Suggests that Glyphosate Does Not Cause Cancer."

March 31, 2015
In recent news, the International Agency for Research on Cancer (IARC) announced that it has labeled the widely used herbicide glyphosate as “probably carcinogenic” to humans in its upcoming review of the product.  Unfortunately, since IARC is an agency of the World Health Organization, the report has been seen as having some credibility.

However the report is not as accurate as it appears.  GMO Answers expert Dr. Michael Greenberg explains his post flaws within IARC's findings:

With regard to glyphosate, it seems the IARC did not consider the overwhelming scientific and medical evidence demonstrating that glyphosate is not a human carcinogen. This includes the largest epidemiological study of farmers ever undertaken, the U.S. National Cancer Institute’s Agricultural Health Study, which failed to find a relationship between glyphosate and cancer. Agencies around the world, including the US EPA and the highly respected German BfR (Agency for Risk Assessment, conducting the EU evaluation of glyphosate) have concluded that there is no risk of cancer with glyphosate use. BfR updated its comprehensive assessment as recently as January 29, 2015 and has criticized the IARC assessment.

In short, the weight of the evidence strongly indicates that glyphosate does not cause cancer— in humans or in animals. The evidence comes from the Ag Health Study which uses a design that is considered the best epidemiology approach for examining the impact of a chemical on actual cancer rates (Blair et al., 2015), and did not find an association with cancer (De Roos et al., 2005).

It is also important to realize that the IARC assessment is what toxicologists call a “hazard assessment,” meaning that a particular chemical might cause a problem under some circumstances.  Paracelsus, the "father" of modern day toxicology, said, "The dose makes the poison.In other words, to translate hazard into risk, you need to know something about dose — a dimension that is critical to understanding potential health impacts of glyphosate on cancer or other clinical conditions. The few animal studies cited by IARC were not repeatable, had tumors at the incidence historically observed for controls and are misquoted by the IARC...

What can we say about exposure to glyphosate?  For the public with exposure via foods, we know that the “worst case” estimates, assuming that permitted crops are treated by all growers and have maximum allowable residues, put us at about 1/5 of the ADI.  Actual use is far less, and most crops have well below maximal levels, so true exposure is far less than this.  In fact, urinary monitoring data available for the US and Europe (which works very well for glyphosate) suggests typical exposures less than 1/100 of the ADI. We also have studies in farmers and farm families (Farm Family Exposure Study) that demonstrate that the majority of farmers had no detectable glyphosate in urine following application, and that wives (all the farmers in this study happened to be male) and children had very low levels and no detectable rise in levels (unless they assisted in application).  Farmers who did apply glyphosate had exposures well within the ADI. 

Overall, it appears that IARC has overreached in its opinion by failing to consider the vast body of literature supporting the notion that glyphosate is not a carcinogen. Further, “the dose makes the poison,” and the IARC, even if they are correct, has failed to place potential hazard into a context of actual risk.  Real-life exposures to glyphosate via food and the environment are small – the ADI is 100 times less than a dose that causes no observable adverse effect in animals, and most people seem to have exposures more than 100-times less than the ADI. Even farmers applying glyphosate fall within the ADI and consumer use exposures, while not studied in the detail we have for farmers, can reasonably be expected to be similar or smaller.

Dr. Greenberg is tenured Professor of Emergency Medicine and Professor of Public Health at the Drexel University College of Medicine (DUCOM) in Philadelphia and Clinical Professor of Emergency Medicine at Temple University School of Medicine. He is the Program Director for the Medical Toxicology Fellowship Training Program at DUCOM, where he also serves as the Chief of the Division of Medical Toxicology.  To read his entire biography visit his profile:

Have more questions on Glyphosate?  Visit GMO Answers Frequently Asked Questions booklet on Glyphosate.