First sold by the agricultural corporation Monsanto in 1974, Roundup weed killer has become popular for home use on the family lawn and also on vast, industrial-scale farms. Beginning in 1996, Monsanto even sold seeds that were genetically engineered to tolerate Roundup so that farmers could apply the herbicide without killing their crops.
However, recent lawsuits have brought Roundup to the public’s attention not as an effective weed killer but rather as a possible health risk. In 2018, a California jury ordered Bayer AG (the company that bought Monsanto) to pay school groundskeeper Dewayne Johnson $289 million in punitive damages after they found the company didn’t warn him that Roundup increased the risk of developing non-Hodgkin lymphoma (NHL). In March 2019, a man who had used Roundup in his yard and later developed NHL won $80 million. Two months later, a couple who had used Roundup for more than 30 years (and both developed NHL) won $2 billion.
Although these settlements were reduced on appeal, several class-action lawsuits are pending. In 2020, Bayer announced that it had agreed to a total payment of more than $10 billion to resolve current and future cases related to Roundup exposure.
Despite the huge amounts of money in play, the scientific evidence for Roundup as a carcinogen isn’t fully settled. Researchers are still figuring if and how Roundup (and other weed killers) cause cancer.
Roundup is effective because it contains an ingredient called glyphosate. When applied to plant leaves, glyphosate inhibits certain plant growth enzymes, eventually killing the plant.
Glyphosate isn’t just used in Roundup — it’s the most commonly used herbicide worldwide, with its use in the United States growing nearly 16-fold between 1999 and 2009. More than 750 products sold in the United States contain glyphosate.
Because glyphosate is used so often, it’s not only found on plants, but in water, soil, and food. It’s also found in humans. Although food and water aren’t regularly tested for glyphosate, small studies suggest that most people have been exposed to some amount of glyphosate. For example, when researchers tested urine samples from a small group of people living in different locations in the United States, they found that 93 percent of the samples contained glyphosate residue.
Scientific studies show mixed evidence for glyphosate as a carcinogen. In 2020, the United States Environmental Protection Agency concluded that glyphosate, when used as instructed, does not increase cancer risk in humans.
However, in 2015, the World Health Organization’s International Agency for Research on Cancer called glyphosate a “probable human carcinogen,” based on evidence from exposure in humans and from the results of experimental animal studies. The IARC found that there was a statistically significant link between glyphosate exposure and developing NHL.
In addition, a 2019 meta-analysis of several studies found that high exposure to herbicides that contained glyphosates was associated with a 41 percent increased risk of developing NHL. The researchers defined “high exposure” as two or more days’ worth of exposure to Roundup per year. The same researchers found that glyphosate use was associated with the development of a certain type of NHL — diffuse large B-cell lymphoma, the most commonly diagnosed NHL type.
These researchers theorized that glyphosates could raise cancer risks by altering the immune system and increasing inflammation, by disrupting sex hormones, or by altering genetic structure.
The people who were awarded Roundup settlements after developing NHL frequently worked with the herbicide as part of their job duties. They didn’t claim to have developed NHL from occasional use or from drinking water or eating food that contained glyphosate.
If you are an agricultural worker or landscaper, you will receive the most exposure to glyphosate. If your use of Roundup or other herbicides that contain glyphosate involves a home flower garden or the occasional dandelion spray, you’re at a much lower risk of heavy exposure.
There are ways to eliminate weeds at home without using a glyphosate-based herbicide. You can use boiling water, salt, and vinegar to kill growing weeds. Putting down layers of mulch, cornmeal, and old newspaper can smother weed seeds before they have a chance to grow. You can also kill weeds the old-fashioned way, by simply pulling them out of the soil.
Several countries, provinces, and cities worldwide have banned or restricted glyphosate-based herbicide use. In the United States, some state and city governments no longer use glyphosate-based herbicides, although they are still legal for private use.
If you decide to use Roundup or other glyphosate-based herbicides in your lawn or garden, limit your exposure by taking the following steps:
Only use Roundup or other glyphosate-based herbicides on sunny, calm days to prevent wind and rain from spreading the herbicide. Do not treat areas near rain gutters or waterways.
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