In March 2015, the World Health Organization's International Agency for Research on Cancer (IARC) gathered seventeen of the world's top cancer researchers to evaluate glyphosate, a primary component of the popular weed-killer, Roundup. The seventeen member work group was led by Dr. Aaron Blair, a recently retired epidemiologist from the U.S. National Cancer Institute.
Over a year-long period, the work group reviewed nearly 1,000 peer-reviewed and published scientific studies. Based on the results of these studies, IARC unanimously classified glyphosate as a Group 2A chemical, "probably carcinogenic to humans." This categorization is given when there is limited evidence of carcinogenicity in humans and sufficient evidence of carcinogenicity in experimental animals. Of the nearly 1,000 chemicals reviewed by IARC to determine the carcinogenic effect, fewer than 100 have received this designation.
The studies reviewed by IARC discussed glyphosate exposure and its connection to various serious health effects. They linked glyphosate exposure to: non-Hodgkin lymphoma, various other types of cancer, kidney disease, heart disease, Parkinson's, Alzheimer's, and chronic respiratory illness. Studies further supported a connection between glyphosate exposure and attention deficit disorder, autism, birth defects and reproductive issues, even infertility.
One of the most significant studies reviewed by IARC was a 65,000 person survey in farming communities in Argentina where Roundup was regularly applied. This study revealed cancer rates nearly four times higher than the national average. Glyphosate exposure was found to most significantly increase the risk of breast, prostate, and lung cancer.
Nearly 30 years prior to IARC's "probably carcinogenic" designation of glyphosate, the US EPA found glyphosate to be a possible carcinogen. In 1985, the US EPA designated glyphosate as a possible carcinogen following tumor growth in rodents exposed to glyphosate. However, after input from Monsanto, the manufacturers of Roundup, the US EPA in 1991 reclassified glyphosate as non-carcinogenic.
Given the recent classification of glyphosate by IARC, the world's leading authority on cancer, the US EPA is again reviewing the possible carcinogenic effects of glyphosate. However, unlike IARC, the US EPA's panel considers unpublished studies. An updated report regarding glyphosate exposure and the risk to humans from the US EPA is expected to be released in spring 2017.
While the US EPA is still contemplating glyphosate's possible carcinogenic effect, California has already taken steps to require warning labels be placed on Roundup. California is the first state to require a warning of Roundup's possible carcinogenic effect on the product label.
The IARC's designation has also caused many countries to ban or place heavy restrictions on glyphosate's use.