The Legal Fallout of Paraquat: 8,000 Lawsuits and Counting

The battle over the herbicide, Paraquat, and Parkinson’s disease has been a decades-long fight surrounding modern agriculture and the health risks that have surfaced as medical discoveries and scientific research about the harmful side effects have evolved. Since its introduction in 1962, Paraquat has been known as a powerful weed killer known for rapidly clearing fields as farmers get ready to plant by eliminating grasses and other unwanted vegetation before crops go into the ground. For many growers, Paraquat’s speed and effectiveness during the preparation process made it a dependable tool in today’s modern farming.

Over time, researchers began noticing a troubling pattern of higher rates of Parkinson’s disease among people who were being exposed to agricultural pesticides, including paraquat.

Multiple Research Studies About Paraquat

There have been several published studies, including one such study in the 2024 International Journal of Epidemiology, “Agricultural paraquat dichloride use and Parkinson’s disease in California’s Central Valley,” which found a strong connection between Parkinson’s and residents and workers who worked within 500 meters of paraquat-sprayed fields. Low-dose contamination exposure was also found in drinking water, and concluded that Parkinson’s was “more likely to develop among people exposed to Paraquat over an extended period of time, according to epidemiological studies.” 

In 2023, another report titled “Paraquat, Parkinson’s Disease, and Agnotology” by Dr. Ray Dorsey and Amit Ray, PhD, highlights a timeline based on a 2022 Guardian report of a suggested cover-up by Syngenta, fearing potential legal liability for long-term, chronic effects of paraquat as long ago as 1975. One company scientist called the situation “a quite terrible problem” for which “some plan could be made”. The article also states “scientists with the Syngenta predecessor Imperial Chemical Industries (ICI) and Chevron Chemical were aware in the 1960s and 70s of mounting evidence showing paraquat could accumulate in the human brain,” and that “internal research showed adverse effects of paraquat on brain tissue, the company withheld that information from regulators while down playing the validity of similar findings being reported by independent scientists.”

This timeline, put together by Dr. Dorsey and Dr. Ray, based on the information from the Guardian, lists a history of internal company documents, events, and historical research findings suggesting early awareness of potential neurological risks associated with paraquat.

Paraquat, the EPA, and the Courts

For decades, Paraquat has been used in fields across America, while the controversy about the side effects of the chemical remained hidden and undisclosed. According to the Environmental Protection Agency (EPA), “Paraquat is highly toxic. One small sip can be fatal, and there is no antidote.” The herbicide continues to be used legally in the United States in spite of the chemical being banned in 32 countries, including the European Union, China, Taiwan, Brazil, Chile, Malaysia, and Peru.

In an EPA report, 2019 draft ecological risk assessment, Paraquat also provided potential risks to local wildlife, mammals, terrestrial invertebrates, terrestrial plants, and algae, making the herbicide a potential environmental hazard even though Syngenta claims that the herbicide is safe when used as directed. 

In 2021, the EPA, during a review, allowed Paraquat to remain on the market in spite of the 2019 report, but imposed additional restrictions to reduce exposure by certified applicators, banning aerial spraying, requiring closed transfer systems, and adding extra training and warning labels for users. The EPA acknowledged published studies linking exposure to Paraquat and Parkinson’s, but stated that current evidence didn’t establish a direct connection between the two. Environmental groups and those representing farmers challenged the decision in 2022 at the United States Court of Appeals for the Ninth Circuit, which ruled the EPA did not fully evaluate the health and environmental risks of the herbicide, forcing the EPA to further review. 

In January 2025, the EPA told the Ninth Circuit it still needed more time to review the health risks that allowed the herbicide to remain on the market. Then, in early January 2026, EPA Administrator Lee Zeldin announced the agency would “freshly reassess the safety” of paraquat and require manufacturers to demonstrate that current uses are safe, effectively bypassing the decision of the Ninth Circuit Court of Appeals and stalling a ban on the herbicide. 

The herbicide will remain legal and available for sale and use in the United States for the next 15 years. 

Currently, there are more than 8,000 cases filed in U.S. Federal and State courts against the makers of Paraquat, Syngenta, Chevron Phillips Chemical Company, and Chevron USA, Inc., (companies that manufactured, distributed, and marketed Paraquat in the United States) for failure to warn about the risks posed by the herbicide, and that Syngenta knew or should have known that chronic exposure to Paraquat could damage the brain, but failed to adequately warn users. 

Because of the extreme number of cases filed across the country, federal courts consolidated them into what is known as multidistrict litigation (MDL) to streamline the process. The MDL was created in 2021 in the United States District Court for the Southern District of Illinois and is known as MDL No. 3004: Paraquat Products Liability Litigation. Some settlements have occurred, including a 187.5 million dollar settlement to resolve an undisclosed number of claims filed against Syngenta. 

Calling it Quits

In a press release dated March 3, 2026, the Switzerland-based company, Syngenta, announced that it will cease production of its herbicide Paraquat (Paraquat dichloride), currently manufactured under the name Gramoxone, at the end of June 2026. 

In a statement made by Mike Hollands, President of Syngenta UK and Head of Syngenta Global Production and Supply, “This decision is about focusing our resources where they deliver the greatest value for our business and our customers.” Sygenta is phasing out production of Paraquat at its site in Huddersfield, UK. Syngenta maintains that paraquat is “safe when used in line with registered label instructions.”  On their website, Syngenta dismisses the claims linking Paraquat and Parkinson’s disease, inviting the public to draw their own conclusions.

In a statement made by the Parkinson’s Foundation Chief Science Officer, James Beck, offered comments on Syngenta’s move to discontinue production of the herbicide: “While Syngenta’s decision to stop manufacturing paraquat is great news, it won’t remove this dangerous product from our food supply until regulators take action and ban it completely,” — because generic competitors are still willing to fill the market gap left by Syngenta’s exit. 

   The Legacy Paraquat Leaves Behind 

For the potential victims of Paraquat and their families, who wait for their day in court, what does this all mean for them? There’s a human cost to all of it. Farmworkers, rural residents, and whole agricultural communities that rely on farming to sustain a living, who suffer from the effects of the disease, face the rest of their lives with Parkinson’s symptoms because of the side effects of exposure. For someone who was just doing their job, the prospect of ongoing medical care for the rest of their lives is not by choice. 

Reflecting on the long-term impact of the paraquat debate, Dr. Michael S. Okun, Distinguished Professor and Director of the University of Florida’s Fixel Institute and co-author of The Parkinson’s Plan, said, “Paraquat will leave a complicated legacy in the Parkinson’s story. Decades of epidemiology and laboratory science have raised serious concerns that certain environmental chemicals may contribute to disease risk. For many patients and families, the debate is not abstract science. It has a lot to do with whether exposures in their past may have helped shape their future.”

The cover-up by Syngenta was allegedly aided in suppressing those risks by a “reputation management” firm called v-Fluence, along with internal documents showing the company withheld damaging internal research from the EPA and worked to discredit a prominent scientist named Dr. Caroline M. Tanner, a neurologist and epidemiologist at the University of California, San Francisco, and the San Francisco VA Medical Center. whose work connected paraquat to Parkinson’s through large epidemiological studies of farmers and pesticide applicators. Her research found that people exposed to pesticides such as Paraquat had significantly higher odds of developing Parkinson’s disease; her information, backed by laboratory evidence, showed that Paraquat could damage dopamine-producing neurons.

There are many similarities between the apparent cover-up of Syngenta, Paraquat, and the involvement of the reputation-management firm v-Fluence, and the actions taken that became central to the lawsuits to suppress information against Bayer and its herbicide, Roundup, which has been linked in litigation to non-Hodgkin lymphoma. Actions taken by these corporations point to business politics and interests continuing to influence the science, raising questions about transparency and regulatory oversight, putting more people at risk for diseases that have no cure.  

Parkinson’s research is growing and is being redefined, expanding into a gut-first, brain-first Parkinson’s disease hypothesis that suggests the disease may originate in the body’s intestinal tract years before the first tremor ever appears and travels to the brain through the vagus nerve. Researchers also believe environmental toxicants, including Paraquat, may be among the triggers that set that process in motion. Researchers are focusing even more on gut-first and whole body approaches to therapies and treatments, exploring how the microbiome, inflammation, and the environment all influence the development and progression of Parkinson’s disease. 

^{Feature image by Chris Dennny/Adobe}

^{Updated 3/6: Quote added by Dr. Michael Okun}