The condemnation from Monsanto came swift and fast.

In March 2015, the International Agency for Research on Cancer — the cancer arm of the World Health Organization — announced that the glyphosate, the active ingredient in Monsanto’s Roundup, was “probably carcinogenic to humans.”

This kind of study might not normally make headlines. But with glyphosate being the most widely-used agricultural chemical in U.S. history, the news report sent shockwaves throughout the industry, and emboldened activists calling for a ban on the herbicide.

Monsanto was quick to shoot down the findings.

“We don’t know how IARC could reach a conclusion that is such a dramatic departure from the conclusion reached by all regulatory agencies around the globe,” said Philip Miller, Monsanto’s vice president of global regulatory affairs.

Not long after, the biotech giant even called for the WHO to retract the report entirely. Their position isn’t surprising, considering that they sell billions of dollars worth of Roundup, which accounts for about a third of their overall sales, each year.

But barely a year later, another study from the WHO and the food arm of the United Nations seemingly contradicted the IARC’s findings, finding that glyphosate was “unlikely to pose a carcinogenic risk to humans from exposure through the diet.

So what’s going on here? First, let’s take a step back.

Monsanto developed glyphosate in the 1970s as a weedkiller, and for the first 20 or so years it was on the market it was used by farmers in targeted areas where they wanted to kill specific vegetation. Using it in a widespread manner across all their crops didn't make sense, because that would likely end up killing all their crops.

But things changed in the 1990s, when Monsanto started selling what they called “Roundup Ready” crops — seeds that had been genetically engineered to grow and withstand exposure to glyphosate. This allowed famers to spray Roundup over their entire cropland without fear of killing their harvest.

Use of Monsanto’s Roundup and other similar herbicides in the United States skyrocketed, from 12.7 million pounds in 1990, to nearly 250 million pounds in 2014. Monsanto’s Roundup Ready crops also became widespread during that time. By 2013, 93% of all soybean crops, 82% of cotton crops, and 85% of corn crops in the United States were herbicide-resistant.

This proliferation of Roundup and Roundup Ready crops has helped Monsanto grow into one of the biggest agrichemical companies in the world. But with a third of their overall sales coming from Roundup, it’s safe to say that any threat to that product poses a serious threat to their bottom line.

Back to those glyphosate studies I mentioned before. Recently, the chairman of the IARC spoke with The Huffington Post, where he doubled down on their findings.

There is not a single example of IARC being wrong, showing something is a probable carcinogen and then later it is proven not to be.
— Alton Blair, Chairman of the International Agency for Research on Cancer

From that same article:

[T]he science on glyphosate is still evolving. [Blair] said that it is common for it to take years, sometimes decades, for industry and regulators to accept certain research findings and for scientists to reach consensus. He likened glyphosate to formaldehyde, which many years ago was also classified by IARC as “probably carcinogenic” to humans before it later was accepted to be carcinogenic.”

This is important, and it highlights a larger problem in how we regulate chemicals. Often, instead of requiring the corporations who develop the chemicals and put them into their products to first prove that they are safe, the burden of proof falls on our regulatory agencies like the Environmental Protection Agency or the Food and Drug Administration. And those agencies often don’t have the resources to test the tens of thousands of chemicals on the market, or the authority to recall them if they’re found to be dangerous.

As a result, we end up spraying farms with nearly 250 million pounds of chemicals that we’re not sure is safe. Not to mention other alarming reports that raise the question of whether the “inert” ingredients in Roundup can cause serious health problems.

But right now, the EPA is deciding whether to re-regulate a number of pesticides, including glyphosate. They’ve already begun to evaluate its safety, and while initial indications point toward them re-approving it, they also acknowledge that much of the research into the whether or not glyphosate is safe comes from before the chemical became so widely-used:

“[With the increased use of glyphosate following the introduction of glyphosate-tolerant crops in 1996, there is a need for more recent studies since a large number of studies were conducted prior to 1996.”

The time for the EPA to act is now, and to us, it’s clear: Unless and until new and independent research can prove it is safe, we need to ban Roundup.