Glyphosate is driving a rift in MAHA. Here’s what the science says about its effects on health

Of all the pesticides available, few have generated as much controversy as glyphosate. Glyphosate, the world’s most widely used weedkiller, is perhaps better known by the brand name Roundup. It works by killing weeds and other unwanted flora that hinder agricultural crops, many of which have been genetically modified to be immune to the deadly effects of glyphosate.

The use of chemical herbicides such as glyphosate has long been denigrated by environmental groups and health advocates, including supporters of U.S. Health and Human Services Secretary Robert F. Kennedy, Jr., who has argued in the past that glyphosate causes cancer.

Then, on Monday, President Donald Trump issued an executive order to boost glyphosate production, sparking an immediate backlash from many within the Make America Healthy Again (MAHA) movement.

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Kennedy, stunning his supporters, supported the president’s order. But other MAHA leaders aren’t so sure: Casey Means, a wellness influencer and Trump’s pick to be the next surgeon general, said she was concerned about the use of “toxic” chemicals to grow food crops during a Senate hearing Wednesday. “We need, as a country, to stop using toxic inputs in our food supply, and we need to study these chemicals more to understand their effects,” she said.

We spoke with two experts to understand what research shows about the health effects of glyphosate and what we know about how it gets into the environment and our bodies.

What is glyphosate?

Glyphosate is an “amino acid inhibitor,” meaning it prevents the growth of weeds by blocking their ability to produce amino acids, which are the building blocks of proteins. The herbicide is commonly applied to crops, such as corn and soybeans, that have been genetically modified to resist its effects.

But glyphosate can absolutely enter our body through our food (cereals and legumes are among the crops most likely to be contaminated by the weedkiller) or through contact with surfaces. People can also inhale it.

Glyphosate was originally manufactured and sold under the name Roundup by Monsanto, which was acquired by German pharmaceutical giant Bayer in 2018. Bayer says it has faced nearly 200,000 claims over alleged harms related to glyphosate exposure, including a high-profile case that the U.S. Supreme Court is expected to consider this year. And earlier this month, Bayer agreed to pay $7.25 billion to settle a class-action lawsuit alleging that exposure to glyphosate played a role in causing non-Hodgkin’s lymphoma, a form of cancer that attacks the lymph nodes.

A Monsanto spokesperson said Scientific American that the settlement did not contain an admission of liability or wrongdoing.

“Leading regulators around the world, including the United States [Environmental Protection Agency] And [European Union] Regulators continue to conclude, based on a broad body of science, that glyphosate-based herbicides – essential tools that farmers rely on to produce affordable food and feed the world – are safe to use and are not carcinogenic,” the spokesperson said.

What research exists on the health effects of glyphosate?

Much of the research on glyphosate has explored its links to cancer. In 2015, the World Health Organization’s International Agency for Research on Cancer (IARC) classified this weedkiller as “probably carcinogenic to humans.” This means there is evidence to suggest that glyphosate poses a cancer risk.

Other public health agencies have disagreed with this assessment. In 2016, the Food and Agriculture Organization of the United Nations and the U.S. EPA determined that glyphosate was not likely carcinogenic.

The research is more nuanced. In 2018, researchers at the National Cancer Institute found “no association” between glyphosate exposure and non-Hodgkin lymphoma in farmworkers. But a year later, in 2019, a meta-analysis found a “compelling link” between glyphosate exposure and cancer. This meta-analysis “was unique because it focused on the highest-exposed groups,” says Lianne Sheppard, lead author of the paper and a professor at the University of Washington who studies the health effects of chemical exposures.

The effects of glyphosate on other animals are also under scrutiny. Studies show that exposure to glyphosate can disrupt honey bees, harming their ability to forage for food, and that the weedkiller could have harmful effects on plants, birds and mammals, according to the EPA.

Part of the reason for the apparent contradictions between IARC, EPA and other agencies is that different experts can assess the merit of certain studies differently, reaching entirely distinct conclusions, says Brenda Eskenazi, professor emeritus of public health at the University of California, Berkeley.

Potential conflicts of interest can also weigh on studies: last year, citing “ethical concerns,” the academic journal Regulatory toxicology and pharmacology retracted an influential 2000 Monsanto-backed study that concluded glyphosate was not carcinogenic.

Sheppard, who served on the EPA panel that examined the carcinogenic potential of glyphosate in 2016, says the scientific evidence for the possible effect of herbicides on human health since then “has strengthened with respect to cancer and other side effects.”

Why don’t we know more about the effects of glyphosate?

Studying glyphosate is difficult: while studies on animal and human cells have shown a link between exposure to the weedkiller and health effects such as cancer, endocrine disruption, oxidative stress, etc., studies on humans are much more difficult to perform.

Glyphosate has a short half-life in the body — by one estimate, just 5.5 to 10 hours — so trying to estimate the effects of glyphosate by looking at levels in a person’s urine, for example, only offers a snapshot of that moment and doesn’t reveal much about its long-term exposure, Eskenazi says. Long-term studies, which might involve the collection and analysis of urine samples taken from participants over a period of time, are logistically difficult and expensive. Scientists might be able to look at geographic data to estimate long-term exposure to glyphosate, but that remains an imprecise measure.

Further research may be underway. Eskenazi says studies focusing on groups, such as pregnant women and fetuses, who might be most vulnerable to glyphosate exposure, as well as research investigating whether glyphosate might affect human fertility and reproduction would be particularly helpful.

“We’re only at the beginning of studying glyphosate, but we definitely need to study it because it’s the most widely used herbicide in the world,” she says. “Even a very small effect, if real, can have a huge impact on public health because large numbers of people would be exposed.”