Can Roundup Weed Killer Really Give You Cancer?

The International Agency for Research on Cancer called the active ingredient in Roundup a "probable" cancer-causer for humans. Credit: Brent Stirton / Getty Images

Earlier this week, the International Agency for Research on Cancer (IARC) officially labeled glyphosate, the active ingredient in the popular weed killer Roundup, a "probable" cancer-causer for humans. First popularized by food giant Monsanto, Roundup has long been the center of debate about potential impact on human health and as such, the Agency's judgment was met with some approval and disagreement. According to prominent food safety and toxicology experts, though, it's too early for everyday consumers to be concerned about the statement — or make any major lifestyle changes in reaction to it.

First, the IARC report is a "hazard evaluation," not a risk assessment, which is the kind of weigh-in that should make us take heed and comes from regulatory agencies like the EPA. This report, on the other hand, is meant to "determine if a substance could cause cancer in some circumstances, at some levels, but it doesn't define the circumstances nor the levels," says Aaron Blair, a retired cancer epidemiologist who previously worked at the National Cancer Institute. A risk assessment, on the other hand, decides whether people can still be around a substance or if it's so awful it should be banned at particular doses.

David Eastmond, a cell biology and toxicology professor at the University of California, Riverside agrees. He says the IARC is a widely respected organization with no regulatory power that doesn't evaluate "risk", or whether a chemical is "likely to cause cancer under conditions to which workers, or the general population, is exposed." He instead suggests waiting for the EPA to evaluate the evidence and determine at what dose the effects are likely to occur — or if they believe that the effects will occur at all. 

Penn State food science professor Josh Lambert also notes the glyphosate levels used in the studies evaluated by IARC were incredibly high — and would relate more to occupational exposure rather than what consumers face every day. "People were exposed at higher levels for longer periods of time, and likely exposed by other routes such as inhalation (rather than orally like consumers)," says Lambert. Furthermore, the epidemiological studies used by the IARC found only "limited rather than sufficient" evidence for cancer in humans, and more evidence in cell lines and rats with rare tumors (which pushed the decision towards probable).

That's not to say glyphosate can't cause harm. "There isn't an absolute certainty but there is enough worry that if you have to be around this stuff you ought to be careful," says Blair. But his and other experts' advice remain as consistent and direct as they've always been: Limit or lower your exposure to glyphosate and other chemicals as much as you can, wash your fruits and vegetables — even organic ones —  and if you work with hazardous substances, follow all the safety precautions (wearing protective gear, washing your hands frequently).


As for food shopping, Lambert and Eastmond don't think you have to switch to organic food based solely on the IARC report. "The amounts in food are likely to be extremely low and not a cause for concern," Eastmond says. "For those who work with glyphosate or use it in their yards, then I would recommend that they exercise a little more caution." He adds there's also a whole host of carcinogens designated by the IARC that are possibly more dangerous than glyphosate, at this point including insecticides, diesel exhaust, alcohol, and even sunlight.