Diquat Dibromide: The Glyphosate-Free Weed Killer That May Be More Dangerous

Roundup's newer bottles say they contain no glyphosate. The active ingredient that replaced it, diquat dibromide, has a toxicology record that is in several ways worse. This article covers what diquat dibromide is, why Bayer switched to it, what the research shows, and where it has already been banned.

Key takeaways

• Diquat dibromide is a contact herbicide in the same chemical family as paraquat. EPA classifies it as Toxicity Category II, "moderately toxic," by ingestion.
• Bayer began replacing glyphosate in U.S. consumer Roundup in 2023 after more than 170,000 lymphoma claims. Friends of the Earth found diquat in every new formulation it tested.
• Using EPA's own chronic reference doses, diquat comes out about 200 times more toxic than glyphosate for long-term exposure.
• Animal studies link diquat to intestinal barrier damage, kidney and liver injury, and cataracts. Two farmer cohorts report an association with Parkinson's disease.
• The EU and UK have banned it. The U.S. EPA kept it registered in a 2019 interim decision with new handler protections.

This article is for education only. I am a certified clinical herbalist, not a physician, and nothing here is a diagnosis or a treatment plan. Toxicology findings described below come from animal studies, poisoning case reports, and regulatory documents, and they do not predict what any individual will experience. If you have been exposed to a pesticide, contact Poison Control or a healthcare provider. Do not start or stop any medication or supplement based on this article.

What is diquat dibromide?

Evidence: strong. Chemistry and acute toxicity values come from regulatory documents and published toxicology.

Diquat dibromide is a fast-acting contact herbicide in the bipyridylium class, the same family as paraquat.⁷ It works by pulling electrons from photosystem I inside the leaf, which generates reactive oxygen and scorches green tissue within hours. Glyphosate, by contrast, is a systemic herbicide that moves through the whole plant and kills it over days.

Its diquat herbicidal uses fall into three groups. It was first registered in 1962 as an aquatic herbicide for lakes and ponds, and it is still one of the most common chemicals sprayed on floating and submerged weeds in U.S. waterways.⁸ Its largest farm use is as a pre-harvest desiccant that dries down potato vines and seed crops so machines can harvest them.⁹ The third group is lawn-and-garden weed killers, where it now stands in for glyphosate.

On acute toxicity, EPA places technical diquat dibromide in Toxicity Category II by the oral route, which the agency's scale calls "moderately toxic," and Category I by the dermal route for the technical material.¹⁰ Published oral LD50 values run from roughly 30 mg/kg in cattle to 120 to 235 mg/kg in rats.^{4, 15} Glyphosate's rat oral LD50 is above 5,000 mg/kg, so on this one measure diquat is more than 20 times as toxic by weight.

Why diquat replaced glyphosate in Roundup

Evidence: strong. Based on Bayer's own announcements and a product survey by an advocacy group, with the ratio traced back to EPA reference doses.

In July 2021 Bayer announced it would remove glyphosate from U.S. residential lawn-and-garden Roundup products beginning in 2023.¹³ The company said the change was about managing litigation risk, not safety. By that point more than 170,000 claims had linked glyphosate to non-Hodgkin lymphoma, and Bayer had set aside more than $10 billion to settle them.

Friends of the Earth, an environmental advocacy nonprofit, surveyed Roundup products on Home Depot and Lowe's shelves in 2024. It identified eight glyphosate-free formulations, and diquat dibromide was in every one, alongside fluazifop-P-butyl, triclopyr, or imazapic.¹² The group compared each chemical to glyphosate using EPA's published figures. Diquat's chronic reference dose is 0.005 mg/kg per day; glyphosate's is 1.0 mg/kg per day. That works out to 200 times more toxic for long-term exposure. On acute toxicity, using the lower 5 percent tail of published LD50 values, diquat came out 27 times more toxic.¹² Friends of the Earth is an advocacy organization and its framing reflects that, but the underlying numbers are EPA's.

My grandfather worked for Southern Ag, a pesticide supply company on the East Coast, and he swore Roundup did not cause cancer. He passed away a few years back. I wonder what he would make of a reformulation that swapped a chemical with a 5,000 mg/kg LD50 for one with a 120 mg/kg LD50 and called it an improvement.

A billion pounds a year

Evidence: moderate. National usage figures come from EPA and USDA surveys; the causal link between pesticide use and chronic disease rates is an inference, not a finding.

U.S. growers apply roughly one billion pounds of conventional pesticide active ingredients each year, a figure EPA has reported in its periodic sales-and-usage reports.¹⁴ The pattern took hold after World War II and became near-universal on corn, soybeans, and wheat by the time USDA began detailed chemical-use surveys in the 1990s. Heavy tillage, monocropping, and high-salt fertilizers burn off soil organic matter and beneficial microbes, and growers then lean harder on quick-acting molecules like diquat to hold yields steady.

GMO crops and the chemical treadmill

Most genetically modified row crops were engineered to survive a specific herbicide. Roundup Ready corn and soybeans tolerate glyphosate, so a field can be sprayed wholesale and only the crop survives. That design ties the seed to the chemical. Cross-pollination between GMO and non-GMO fields is documented, and it has produced patent lawsuits against farmers whose crops picked up the trait. I avoid GMO foods where I can. These crops are new to human diets, and I do not think two or three decades without a detected problem is the same as proof of safety.

A conversation at the farmers market

I asked a peach grower at a local market what he sprayed, since I saw no organic or no-spray signage. He named a few products and told me he had eaten these peaches his whole life. I did not ask about his health. What I can say is that the United States uses more pesticide by volume than any nation except China, according to FAO tallies, and reports the highest chronic disease burden among wealthy countries. Pesticides are not the only cause. The epidemiology on farm workers suggests they are part of it.

What the research says about diquat dibromide

Evidence: moderate to strong for gut and organ toxicity (animal studies and human poisoning cases); moderate for Parkinson's (two observational cohorts); strong for cataracts (chronic feeding studies that set EPA's reference dose).

Full citations are in the sources list at the end.

Area	What the studies report
Gut lining and microbiome	Two 2025 reviews, one in Antioxidants and one in Frontiers in Pharmacology, summarize animal work showing diquat drives oxidative stress in intestinal cells, breaks down tight-junction proteins (ZO-1, claudin, occludin), lowers Lactobacillus counts, enriches pathogenic bacteria, and lets endotoxin cross into circulation. Villus atrophy and systemic inflammation follow.1, 2 Diquat is used deliberately in pig and mouse research as a standard tool for inducing oxidative gut injury, which tells you how reliable the effect is.
Kidney, liver, lung	A 2018 review of human poisoning cases and experimental data identifies the kidney as the main target organ, driven by redox cycling. Liver inflammation and lung injury are also recorded. There is no antidote for diquat poisoning.3
Parkinson's disease	The French AGRICAN cohort (over 180,000 farmers) found lifetime diquat use associated with higher odds of Parkinson's, with odds ratios across the flagged pesticides ranging from 1.31 to 1.57, strongest in the longest-exposed farmers.5 A 2024 California study of 829 Parkinson's patients found diquat and paraquat each independently associated with the disease.6 Mechanistic work points to dopaminergic neuron loss.
Eyes and development	Cataracts in long-term rat and dog feeding studies are the effect EPA's chronic reference dose is built on.10, 15 Rat studies also reported skeletal variations in fetuses at doses that were toxic to the mothers.15 EPA's 2002 review found no evidence of endocrine disruption.9

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Where diquat is banned, and what EPA did in 2019

Evidence: strong. Taken directly from the EU regulation and EPA's registration review docket.

The European Commission declined to renew diquat's approval in October 2018 under Regulation (EU) 2018/1532, citing risks to workers, bystanders, and birds. Sales ended in 2019 and remaining stocks had to be used up by early 2020.¹¹ The United Kingdom carried the ban forward after leaving the EU. Syngenta still manufactures diquat in the UK for export.

The U.S. record is different. EPA reregistered diquat dibromide in 1995 and completed a tolerance reassessment in 2002.^{9, 10} In December 2019 the agency issued an interim registration review decision that kept the chemical on the market but added protections: mandatory protective eyewear and respirators for occupational handlers, a ban on backpack sprayers for both land and aquatic use, and lower application rates for crop burndown, ornamentals, and surface aquatic weeds.^{7, 8} Product labels are still being amended to match that decision as of 2026, and the endangered species assessment has not been completed. Diquat remains a general-use pesticide, meaning anyone can buy it at a hardware store without a license.

The original version of this article said EPA had not looked at diquat in over 20 years. The 2019 interim decision shows the agency did review it. The review left it on shelves.

What researchers have tested against diquat gut injury

Evidence: preliminary. Animal models only. This is a summary of what has been studied, not a protocol.

Because diquat is the standard tool for creating oxidative gut injury in lab animals, a large body of research exists on what blunts that injury in pigs, mice, and rats. The 2025 Antioxidants review lists probiotics (including Lactobacillus strains and Bacillus spores), plant antioxidants such as hydroxytyrosol from olives and curcumin, selenium, and short-chain fatty acids like butyrate as interventions that restored tight-junction proteins and reduced inflammatory markers in these models.¹ The Frontiers review adds that these compounds act mostly through the Nrf2 antioxidant pathway.²

None of this has been tested in people exposed to herbicide residue at dietary levels, and the doses used in pig studies are far higher than anything in food. What the research does show is that the intestinal barrier is where diquat does its first damage. If you want the background on how that barrier works and what weakens it, I wrote about it in What is leaky gut?

Reducing exposure, and why I keep pushing regenerative farming

Evidence: mixed. Label-reading and organic certification rules are documented fact. The farming section is my opinion.

Read the label

"Glyphosate-free" on the front of a weed killer tells you what was removed, not what was added. Turn the bottle over and look for diquat dibromide, paraquat, fluazifop-P-butyl, triclopyr, or imazapic in the active ingredients panel.^{12, 14} For lawns and gardens, mechanical weeding, mulch, flame weeding, and dense planting do the same job without any of them.

Food residues

Diquat's largest crop use is drying potato vines before harvest, and it is also labeled for seed crops and several other fields.⁹ USDA organic certification prohibits it, so certified organic and Regenerative Organic potatoes avoid that exposure route. Because diquat is also an aquatic herbicide applied directly to lakes and ponds, it is one of the pesticides worth checking your local water report for. My water filter guide covers which filter types handle pesticide residues.

Policy

The EU got diquat off the market with an ordinary non-renewal decision. The U.S. path runs through EPA's registration review docket, which accepts public comment, and through the state level, where California has moved faster than the federal government on the closely related paraquat.

Regenerative farming

Switching from chemical agriculture to regenerative practices costs more up front and will need new equipment at scale. I still think it is the only direction that protects long-term food security. Topsoil erosion outpaces soil formation across much of the U.S. grain belt, and every desiccant pass and bare-soil winter makes that worse. I support regenerative small farms where I can, and I hope to start one myself once we buy land. For now I work a very small garden at our rental. If you have farmers you buy from, ask what they spray. Most of them have never been told what is in the bottle either.

Frequently asked questions

Is diquat safer than glyphosate?

Not by the regulatory numbers. EPA's chronic reference dose for diquat is 200 times lower than glyphosate's, and its acute oral toxicity is more than 20 times higher by weight. Glyphosate's cancer link is the reason it was pulled from consumer Roundup, but diquat has its own record on kidney, gut, eye, and neurological effects.

Is diquat banned in the United States?

No. EPA reviewed diquat dibromide in 2019, kept it registered, and added handler protections and rate cuts. It remains a general-use pesticide sold to the public.

Which Roundup products contain diquat dibromide?

Friends of the Earth found it in all eight glyphosate-free Roundup formulations it surveyed in 2024. Check the active ingredients panel on any specific bottle, since formulations change and some glyphosate-based Roundup products remain on shelves.

Does diquat stay in the soil?

Diquat binds tightly to clay and organic matter and stops being active once it hits soil, which is why it does not carry over to the next crop. That binding also means it persists in sediment for a long time rather than breaking down.

Sources

1. He J, Tang Q, Liu YC, Wang LJ, Chai YF. Impact of diquat on the intestinal health and the composition and function of the gut microbiome. Antioxidants. 2025;14(6):721. doi:10.3390/antiox14060721. Authors at Tianjin Medical University General Hospital; no conflicts declared.
2. He X, Cai Y, Jia Y, et al. Effect of diquat on gut health: molecular mechanisms, toxic effects, and protective strategies. Frontiers in Pharmacology. 2025;16:1562182. doi:10.3389/fphar.2025.1562182.
3. Magalhães N, Carvalho F, Dinis-Oliveira RJ. Human and experimental toxicology of diquat poisoning: toxicokinetics, mechanisms of toxicity, clinical features, and treatment. Human and Experimental Toxicology. 2018;37(11):1131-1160. doi:10.1177/0960327118765330.
4. Clark DG, Hurst EW. The toxicity of diquat. British Journal of Industrial Medicine. 1970;27(1):51-55. PMID 5418919. Both authors were employed by ICI, the original manufacturer of diquat, at the time of publication.
5. Pouchieu C, Piel C, Carles C, et al. Pesticide use in agriculture and Parkinson's disease in the AGRICAN cohort study. International Journal of Epidemiology. 2018;47(1):299-310. doi:10.1093/ije/dyx225.
6. Paul KC, Krolski C, Ritz B, et al. Agricultural paraquat dichloride use and Parkinson's disease in California's Central Valley. International Journal of Epidemiology. 2024;53(1):dyae004. doi:10.1093/ije/dyae004.
7. U.S. Environmental Protection Agency. Diquat Dibromide Interim Registration Review Decision, Case Number 0288. December 2019. Docket EPA-HQ-OPP-2009-0846. regulations.gov.
8. U.S. Environmental Protection Agency. Diquat Dibromide Fact Sheet: Aquatic Herbicide. July 2025. epa.gov.
9. U.S. Environmental Protection Agency. Fact Sheet for Diquat Dibromide, Tolerance Reassessment Progress and Risk Management Decision (TRED). May 2002. epa.gov.
10. U.S. Environmental Protection Agency. Reregistration Eligibility Decision (RED) for Diquat Dibromide. EPA 738-R-95-016. 1995. Toxicity categories confirmed in EPA's later human health risk assessment, docket EPA-HQ-OPP-2009-0920-0008.
11. Commission Implementing Regulation (EU) 2018/1532 of 12 October 2018 concerning the non-renewal of approval of the active substance diquat. Official Journal of the European Union. L 257/10.
12. Friends of the Earth. New Roundup, New Risks. October 2024. foe.org. Friends of the Earth is an environmental advocacy nonprofit funded by member donations and foundation grants; it campaigns against pesticide use.
13. Bayer AG. Bayer provides update on path to closure of Roundup litigation. Press release, 29 July 2021.
14. Brosnan J, Bumgarner N, Bowling R, et al. Update on Roundup-Branded Herbicides for Consumers. University of Tennessee Extension Publication W 1237. 2024. Annual U.S. pesticide volume from EPA, Pesticides Industry Sales and Usage report series.
15. California Department of Pesticide Regulation. Diquat Dibromide Risk Characterization Document. 17 August 1994. cdpr.ca.gov.