Monsanto and its supporters point to a number of studies that found no evidence of a link between Roundup and any form of cancer. For example, a 2016 study funded by Monsanto “did not find support in the epidemiologic literature for a causal association between glyphosate and [non-Hodgkin lymphoma (NHL)] or [multiple myeloma (MM)],” two types of cancer commonly associated with the substance. Other studies have similarly failed to discover a connection between Roundup and cancer.
Nonetheless, in 2015, the International Agency for Research on Cancer (IARC), the World Health Organization’s international agency, classified glyphosate as “probably carcinogenic in humans,” even while noting that there was “limited evidence” of a link between glyphosate and non-Hodgkin’s lymphoma. There are two primary reasons for why IARC researchers classified the weed killer as a carcinogenic chemical, despite what some have called thin evidence:
- Animal studies – specifically, studies of mice and rats – demonstrated a possible link between glyphosate and cancerous tumours.
- Laboratory studies of the damaging effects of glyphosate on DNA showed “mechanistic evidence” that the weed killer can indeed damage DNA in human cells upon exposure.
A French court cited the IARC’s decision and several scientific health studies when it enacted an immediate ban of Monsanto’s product Roundup Pro 360 earlier this year. Politicians in France have also taken steps to reduce the amount of glyphosate use in the country. Though a complete ban on glyphosate products has been deemed unwise in an effort to protect farmworkers and the country’s economy during the change.
Other groups have called the IARC’s classification into question, claiming that it ignored various studies. While this is true (scientists at the IARC do not consider studies funded by privately held companies, as well as studies that meet certain other criteria), the IARC has not retracted or changed its classification.
Other regulatory agencies have made their own determinations. For example, both the U.S. Environmental Protection Agency (EPA) and the European Food Safety Authority (EFSA) found that glyphosate was probably not carcinogenic. However, the California Office of Environmental Health Hazard Assessment lists the chemical as a “known carcinogen,” largely based on the IARC’s classification.
The claim that glyphosate causes cancer has led to the filing of hundreds of Roundup lawsuits in state and federal courts across the United States. So far, two state court juries and one federal court jury found verdicts in favor of the plaintiffs against Monsanto and their parent corporation Bayer. In total, Bayer and Monsanto have been ordered to pay nearly $2.2 billion in damages for these three trials. While the companies continue to file appeals, many more lawsuits are still underway. Though these initial verdicts grant hope to plaintiffs, given the unclear state of scientific evidence, the amount to which Monsanto could be held liable in future cases and appeals remains to be seen.