Roundup weedkiller may no longer contain its most notorious ingredient in residential formulas, but its replacement could be even more dangerous.

Once seen as a safer alternative to glyphosate, diquat is now found in some of Bayer’s Roundup weedkiller products and may pose its own serious health risks. A review published in Frontiers in Pharmacology links diquat to gut damage, microbiome disruption and potential harm to internal organs.

“From a human health perspective, this stuff is quite a bit nastier than glyphosate so we’re seeing a regrettable substitution, and the ineffective regulatory structure is allowing it,” Nathan Donley, science director with the Center for Biological Diversity, told The Guardian in a recent interview.

Diquat is a contact herbicide that kills plants by damaging their cells and creating oxidative stress. It’s been used in agriculture for decades and is banned in several countries. The chemical acts fast, but the same mechanism that kills weeds may also harm the human body.

New Concerns Over Roundup’s Herbicidal Ingredient

The Frontiers in Pharmacology review analyzed dozens of past studies. It focused on how diquat affects your body and raised concerns about the weedkiller.

Researchers found that diquat:

  • Can harm your liver, kidneys and lungs
  • Damages your gut lining
  • Kills off good gut bacteria, including beneficial bacteria like Lactobacillus
  • Triggers inflammation throughout your body

The authors suggest that more research is needed on low-dose, long-term exposure in humans. Still, the review challenges the idea that diquat is a safer alternative, especially for homeowners using the newly formulated Roundup.

Same Bottle, Different Risks

Bayer began reformulating its residential Roundup products in 2023, removing glyphosate and replacing it with alternative ingredients like diquat. However, the packaging remained virtually unchanged, concerning experts who warn that consumers may not realize what they are using.

Those who use Roundup are encouraged to read the warning labels and only use the herbicide as directed. Diquat, for instance, is not approved for use around edible plants.

Although the warning labels on the product are required to include active pesticide ingredients, consumers may overlook the differences due to the seemingly unchanged packaging.

Bayer maintains that its glyphosate products are not harmful. “We have taken this action [to reformulate] exclusively to manage litigation risk and not because of any safety concerns,” the company wrote in a statement on its website.

Thousands of Lawsuits Are Pending

Bayer, which acquired Roundup developer Monsanto in 2018, has faced more than 170,000 lawsuits in multidistrict litigation over glyphosate-based products as of July 2025. Plaintiffs allege they developed non-Hodgkin lymphoma and other health issues after exposure to glyphosate herbicides like Roundup.

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The U.S. Environmental Protection Agency maintains that glyphosate is “unlikely to be a human carcinogen” when used as directed. But the World Health Organization’s International Agency for Research on Cancer said that glyphosate is “probably carcinogenic to humans,” a contradiction that helped fuel years of litigation.

With diquat under growing scrutiny, public health advocates warn that the underlying risks may not have disappeared just because glyphosate use isn’t as prevalent.