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If there’s one thing that people love to hate, it’s a chemical with a long name. Never mind that, in the words of the inimitable Tim Minchin, “everything is chemicals.” We are always more afraid of something if it sounds like an artificial concoction rather than a natural product, even though asp venom and great white sharks are perfectly natural.
A great example is glyphosate. Perhaps best known as the main ingredient in Monsanto’s RoundUp herbicide, glyphosate is one of the most commonly used methods of handling weeds on farms and elsewhere. It is a key part of modern agriculture, to the point that imagining a food system that operates without it is incredibly challenging. Yet, glyphosate is also the subject of much debate. Scientists worry about the effects that it could have on our bodies, and some portion of people the world over are convinced that it is horrible poison.
You can see this in the recent news. Donald Trump announced measures aimed at boosting glyphosate production on U.S. soil, including protections for companies making the stuff, which Robert F. Kennedy Jr. then expressed support for. This goes strongly against the head of Health and Human Services’ previously stated views on the chemical and led to impressive outrage from his closest adherents, including cries that he is now participating in chemical warfare against the American people. RFK Jr. then went on Joe Rogan’s podcast and made some wishy-washy remarks about the whole thing, including that glyphosate is “not a good thing to have in your food.”
You might try to tune out MAHA infighting but still find yourself worrying about glyphosate: It has been linked to cancer. What the science says on the question of Is glyphosate harmful? is complex. Luckily, there is a pretty clear take-home message for most of us and, I think, an area where people could direct their concern without calling for an overhaul of the entire agricultural system.
Glyphosate is a fascinating chemical. Developed in the 1970s, it has been widely used for decades because it is both highly effective at preventing weeds from growing and, acutely, very safe. Acute in this context means that it’s quite difficult to poison yourself with glyphosate—as far as immediate danger goes, the chemical is about as hazardous as table salt. When it comes to something that is sprayed on plants that will eventually make their way to your plate, this is great news.
For decades, however, people have been worrying that small doses of glyphosate ingested over the long term can cause cancer and other health issues. And this is where it gets really complicated. Many things that we can ingest in high doses in the short term can cause massive problems over time. For example, cigarettes. You can smoke three packs of cigarettes in one day and experience no negative impacts. (Well, no long-lasting ones—you might feel woozy and have a cough.) But smoke one cigarette a day for a couple of decades, and the situation is much more problematic.
The first thing to understand here is that you, the person who is reading this article, are almost certainly not at risk from glyphosate. This is a matter of dose. A 2021 study looked at the amount of glyphosate based on U.S. diets—the average person gets around 0.00004 grams a day from food and water. People who eat lots of high-glyphosate foods may ingest up to 0.001 grams.
As far as the current scientific literature goes, the concern is about amounts that are much higher than this. The current U.S. Environmental Protection Agency safety threshold—the dose that the EPA considers to be safe for general consumption—is set at about 0.007 grams a day for the average adult. That means that even people who ingest extremely high levels of glyphosate via their food get far less than the amounts that we are concerned about. The most conservative scientific assessment I am aware of looked at doses of glyphosate in rodents that were equivalent to 0.038 grams a day in humans—and found barely detectable and inconsistent effects in rodents at a comparable dose.
So for you, eating your food, glyphosate is probably not an issue. The real question is whether much higher doses of the chemical could be problematic for agricultural, forestry, and similar workers who spray the stuff on a daily basis. If you have a job doing specifically that, things get stickier. People who work with glyphosate tend to get much higher doses of the chemical than your average person, and there is certainly some evidence that very, very high doses could be a problem. The study I cited above also looked at doses of glyphosate that were equivalent to around 0.5 grams a day for an adult human—500 times as high as the highest levels people get from food—and found some worrying signals of harm.
The problem here is that the evidence is inconsistent. There are several rodent studies that suggest some harms of doses, and several that do not. One of the most famous studies that showed harm was retracted after concerns were raised regarding the integrity of the data.
We’ve also got some epidemiological evidence for the potential risks of glyphosate. This mostly takes the form of what’s called a case-control study. This is when you identify people who have or have had a disease and look back at their past exposures to see if they might be related to the illness. For example, a Swedish study from a few years ago identified people with non-Hodgkin lymphoma and reviewed their past exposure to herbicides and pesticides. The authors found that people with NHL had about double the odds of being exposed to glyphosate than a control group who didn’t have the disease.
But this type of study has some fairly obvious drawbacks. In particular, researchers have to ask subjects about their past exposures, and people are terrible at remembering things. In the Swedish study above, many of the participants had been diagnosed decades earlier. Some of them were dead, and their families answered the questionnaires about past glyphosate exposure in their stead. This doesn’t give us much confidence in the reliability of the results.
Another way to do this sort of research is to ask people how much glyphosate they are exposed to, then follow up with them over time. There’s currently only one big study that I could find that did this, the Agricultural Health Study. In 2018, after about 15 years of follow-up, the researchers reported that glyphosate use was not associated with any of the cancers they had examined. There was one statistically significant result out of the dozens of tests they ran, which is about what we’d expect to see purely by chance. Overall, this suggested that reported glyphosate exposure was not connected to cancer of any kind in agricultural workers.
On top of all of this noise are several studies that have measured urine biomarkers for glyphosate and associated those with health outcomes. Some of these seem to indicate that people who have higher levels of glyphosate in their urine score worse on memory tests, have slightly more heart disease, and are generally less well than people who have less glyphosate in their bodies. Others, however, show no negative effects from the chemical.
So is glyphosate bad for us? As with every chemical, the answer is that it depends on the dose. At the level that consumers are exposed to, there is almost certainly no risk of harm. There may be issues caused by glyphosate at realistic doses that people get from working with the chemical. We aren’t sure, but it certainly seems possible.
All of this brings me back to the recent uproar over RFK Jr.’s support (and semi-support) for Trump’s pro-glyphosate policies. The main scientific concern with glyphosate is industrial exposure—but I haven’t heard anyone even mention workers in this discussion. We could likely substantially reduce risk by ensuring that basic protective equipment is provided to workers who spray it on plants. But people love fighting about whether chemicals are good or bad. Talking about the importance of gloves and masks is less dramatic and interesting.
