For years the agrochemical giant Monsanto has insisted publicly that the chief ingredient in its top-selling weedkiller Roundup is safe and not carcinogenic to humans.

Glyphosate is “safe,” affirmed a company spokesman in 2013, after a study linked the chemical to an array of health problems, including Parkinson’s disease, infertility and cancer. “There is no evidence that glyphosate causes cancer, even at very high doses,” a Monsanto spokesman told the Intercept in early 2016. 

Now, a trove of recently released Monsanto emails show the chemical’s purported safety was the subject of ongoing internal debate. Scientists on Monsanto’s payroll repeatedly urged company officials to stop calling glyphosate “safe.”

At the same time, Monsanto orchestrated concerted attacks to discredit scientists and individuals who questioned the safety of glyphosate.

Glyphosate is the most widely used weedkiller in the United States, but the controversial product has been banned in at least 18 countries over health risk concerns.

In 2015, the International Agency for Research on Cancer of the World Health Organization categorized glyphosate as “probably carcinogenic to humans.” A team of University of Washington researchers found exposure to glyphosate increased a person’s risk of non-Hodgkin's lymphoma by 41 percent.

In the last year, U.S. juries have awarded more than $2 billion to plaintiffs who claimed glyphosate caused their cancer, and an estimated 18,000 cases are pending.

Attorneys for the plaintiffs obtained the Monsanto emails, which show a pattern of discrediting scientists and organizations that questioned Roundup’s safety, while bankrolling a virtual army of researchers and journal reviewers to write positively about Roundup and glyphosate. 

The entire cache of emails can be found here.

The emails suggest Monsanto-affiliated scientists were well aware that glyphosate’s safety was questionable. In a 2014 email exchange, Monsanto toxicologist Donna Farmer warned a company spokesperson to not call glyphosate safe. “We cannot say it [glyphosate] is ‘safe’...we can say history of safe use, used safely etc,” Farmer wrote.

She encouraged the spokesperson to instead call the chemical “one of the most thoroughly tested herbicides,” and one that “poses no unreasonable risks to people” when used according to directions.

In 2015, after an arm of the World Health Organization labeled glyphosate as “probably carcinogenic to humans,” the Monsanto emails show the company immediately launched a campaign to help restore glyphosate’s tarnished reputation.

In one email exchange, company officials discussed an upcoming presentation at the Society for Risk Analysis Annual Meeting in Virginia meant to emphasize the safety of glyphosate

When one company consultant, Ashley Roberts, suggested they title the presentation “An Expert Panel Concludes There is No Evidence that Glyphosate is Carcinogenic to Humans,” another consultant, an epidemiologist at the University of Birmingham, warned: “We can’t say ‘no evidence’ because that means there is not a single scrap of evidence, and I don’t see how we can go that far.” 

A former Monsanto epidemiologist John Acquavella agreed, writing “you can’t say there’s no evidence” that glyphosate causes cancer.

Emails from 2010 show the company didn’t actually know whether its Roundup formulation causes cancer in people because it had never tested it despite claiming it was safe to use. Emails also show the company was aware back in 2012 that Roundup may contain trace amounts of arsenic. Monsanto toxicologist Farmer, however, didn’t believe the amount of arsenic posed a health hazard to people.

Roundup has been on the market since 1974. More than 1.6 billion kilograms of glyphosate has been sprayed in the U.S. since that time, according to a 2016 paper in the journal Environmental Science Europe

For years, the U.S. Environmental Protection Agency has stated that glyphosate does not pose a public health risk. However, earlier this year, an arm of the U.S. Department of Health and Human Services issued a draft glyphosate toxicological profile noting that 20 studies had linked glyphosate to cancer in humans.

In response to the mounting controversy over glyphosate, Bayer AG, which recently purchased Monsanto, announced in June it would spend $5.6 billion over the next decade to find an alternative to glyphosate. 

However, just last year, Bayer had stood by glyphosate, stating the chemical has a “history as a safe and efficient weed control tool."