Monsanto's Controversial Weed Killer Roundup Does Not Cause Cancer, New Study Shows

The active ingredient in Roundup does not cause cancer, according to scientists at the National Cancer Institute. Researchers followed over 50,000 people who used pesticides to see if the ones who used Roundup developed any kind of cancer. The results were published Thursday in the Journal of the National Cancer Institute.

Farmers, the NCI's website states, have generally lower death rates than the average American, in part because their job requires more activity. However, the rates of some cancers are higher. "Farmers, farmworkers and farm family members may be exposed to substances such as pesticides, engine exhausts, solvents, dusts, animal viruses, fertilizers, fuels and specific microbes that may account for these elevated cancer rates," the Institute notes. The same cohort of people has been used to evaluate the potential increased cancer risks associated with pesticides before.

However, they didn't find any association between glyphosate, the active ingredient in Roundup, and most cancers. Only "some evidence" supported a link between the chemical and one particular type of cancer, acute myeloid leukemia. Even that association was not statistically significant.

Monsanto's vice president of strategy, Scott Partridge, told Reuters that the study "definitively demonstrates in a real-world environment that glyphosate doesn't cause cancer."

Pesticide spray
A farmer sprays pesticides on his crops in Bailleul, in northern France, on June 15, 2015. French Ecology Minister Ségolène Royal announced on June 14, 2015, a ban on the sale of American biotechnology giant Monsanto’s popular weed killer Roundup, which was classified as “probably carcinogenic to humans” by the United Nation’s International Agency for Research on Cancer (IARC). Monsanto denies the chemical is cancer causing. PHILIPPE HUGUEN/AFP/Getty Images

But the study will probably not persuade everyone—in part because it contradicts other evaluations of the compound's potential to cause cancer. The International Agency for Research on Cancer, an organization best known for its evaluations of the evidence about whether various chemicals may cause cancer in humans, said in 2015 that glyphosate was a probable carcinogen. That categorization means that the evidence suggests a link between the chemical and cancer—but is still inconclusive. Earlier this year, California also added glyphosate to its list of chemicals that can cause cancer.

The findings could impact an ongoing class-action lawsuit about the chemical. Nearly 200 people have sued Monsanto, the company that makes Roundup, alleging the weed killer gave them cancer. That case is just one of the ones Monsanto is currently fighting over its products; the company sued Arkansas over restrictions on a different pesticide: dicamba. The Wall Street Journal has reported on the suit and the ban, which stems from accusations that dicamba drifted onto crops grown by farmers who don't use Monsanto's resistant seeds, which damaged them.

Since Roundup-tolerant crops were introduced in 1994, use of the weed killer has increased about fifteenfold, according to researchers at the University of California, San Diego, who published a study about the amount of the chemical found in urine samples in the Journal of the American Medical Association in October. That study found that in 100 people living in Southern California, the level of glyphosate increased significantly between the mid-1990s and the mid-2010s.

On Thursday, regulators in the European Union declined to reauthorize the use of glyphosate for five more years, The New York Times reported. The vote was close, and actually there were more votes cast in favor of renewing the authorization than declining it. However, it didn't reach the required majority.