Chlorpyrifos Pesticide Side Effects Research Highlights Decades of Parkinson’s Disease Risks

Series of Parkinson’s disease lawsuits have been filed recently alleging routine exposure to Lorsban, Dursban and other chlorpyrifos products caused individuals to develop serious neurological injuries.

After decades of chlorpyrifos use in Gulf War military camps, homes, businesses and agricultural operations throughout the United States, new research has identified evidence that the pesticide may cause neurological side effects, supporting a growing number of Chlorpyrifos Parkinson’s disease lawsuits now being filed.

Chlorpyrifos is an organophosphate insecticide introduced in the 1960s and sold under brand names including Dursban, Lorsban, Cobalt, NuFos, Bolton, Stallion, Lock-On and Warhawk.

The pesticide has been heavily used across multiple industry settings. Chlorpyrifos was used during the Gulf War to control insects around military camps and facilities, and was also widely applied in homes, schools, businesses and other properties for termite treatments and general pest control.

Agricultural formulations were sprayed on a broad range of crops, exposing farmers, pesticide applicators, equipment workers and nearby residents through mixing, spraying, contaminated equipment, drift and residue.

For years, that widespread use continued even as concerns mounted over whether chlorpyrifos could harm the human nervous system at exposure levels far below those associated with immediate pesticide poisoning.

Chlorpyrifos Parkinson’s Disease Lawsuits

Federal regulators have repeatedly moved to restrict chlorpyrifos, including a 2021 EPA ban on its use in food and crops that was later overturned by a federal appeals court. Although those uses were reinstated, the agency has continued to consider additional restrictions as concerns about the pesticide’s neurological effects have intensified.

However, those concerns now extend beyond developmental injuries. A growing body of research links chlorpyrifos exposure to oxidative stress, mitochondrial dysfunction and the loss of dopamine-producing brain cells, with one recent study finding that long-term residential exposure was associated with more than double the risk of Parkinson’s disease.

As a result, chlorpyrifos lawyers are investigating Parkinson’s disease claims against the pesticide manufacturers for Gulf War veterans, farmers, agricultural workers, pesticide applicators, pest control technicians and others who developed Parkinson’s disease after repeatedly handling the pesticide or spending time near areas where it was applied.

Chlorpyrifos Side Effect Studies

The case against chlorpyrifos does not rest on a single study. Researchers have approached the question from several directions, examining disease rates among exposed individuals, testing the pesticide in laboratory models and revisiting older industry studies that regulators relied on for years.

Together, the findings provide evidence that chlorpyrifos may increase the risk of Parkinson’s disease, damage the same brain cells destroyed by the condition and produce neurological effects at exposure levels previously characterized as safe.

Chlorpyrifos Exposure Linked to 2.5 Times the Parkinson’s Disease Risk

The most direct evidence emerged from a 2025 study published in Molecular Neurodegeneration, titled “The pesticide chlorpyrifos increases the risk of Parkinson’s disease“. Researchers compared 829 people diagnosed with Parkinson’s disease with 824 individuals who did not have the condition.

Using California pesticide records and decades of residential and workplace histories, researchers found that long-term chlorpyrifos exposure was associated with more than a 2.5-fold increased risk of Parkinson’s disease. The likelihood of developing the condition also rose as the duration of exposure increased.

The researchers then went a step further. In mice and zebrafish, chlorpyrifos caused movement problems, brain inflammation, abnormal alpha-synuclein buildup and the loss of dopamine-producing neurons, which are the same cells progressively destroyed by Parkinson’s disease.

That combination of human and laboratory evidence makes the study particularly important to the lawsuits. It not only identified an increased risk among exposed individuals, but also demonstrated how chlorpyrifos may produce the underlying brain damage.

Chlorpyrifos Disrupted Genes Tied to Parkinson’s Disease

Earlier research had already raised concerns that chlorpyrifos could interfere with biological processes involved in Parkinson’s disease.

A 2011 study titled “Developmental exposure to organophosphates triggers transcriptional changes in genes associated with Parkinson’s disease in vitro and in vivo” exposed developing neuron-like cells to chlorpyrifos and examined changes in genes associated with the condition. Researchers found significant alterations in the activity of several Parkinson’s-related genes.

The findings suggest chlorpyrifos may disrupt neurological functions long before a person develops visible symptoms. That is relevant to claims involving Parkinson’s disease, which may not be diagnosed until years or decades after the pesticide exposure occurred.

Independent Researchers Challenged Dow’s Human Safety Study

One of the studies used for years to evaluate chlorpyrifos safety involved volunteers who were intentionally given measured doses of the pesticide.

Dow Chemical, the manufacturer of Lorsban and Dursban, sponsored that study in 1972. The researchers concluded that participants exposed below a certain dose showed no harmful effects, and federal regulators later relied on that finding when setting acceptable exposure levels.

University of Washington researchers revisited the study in 2020 and found that the original analysis left out important information about the participants’ health before they were exposed. Without those baseline measurements, it was more difficult to recognize changes that occurred after the pesticide was administered.

When the missing information was included, the data showed effects at doses Dow had characterized as causing no harm. The researchers also concluded that modern statistical methods would have detected changes even among participants who received the lowest dose.

The reanalysis raises questions about whether regulators were given an accurate picture of the risks when they established chlorpyrifos exposure limits.

Independent Review Found Brain Changes at Every Dose Tested

Questions were also raised about an animal study Dow relied on to argue that chlorpyrifos did not cause developmental brain damage.

That study, titled “Safety Evaluation of Pesticides: developmental neurotoxicity of chlorpyrifos and chlorpyrifos-methyl“, involved pregnant rats that were given different doses of chlorpyrifos. Researchers then examined the brains of their offspring and concluded that the pesticide did not cause a distinct pattern of developmental neurotoxicity.

In 2018, independent scientists reexamined the underlying data and found changes in a measurement of the cerebellum at every chlorpyrifos dose tested. The cerebellum is the part of the brain involved in movement, coordination and balance.

The researchers also identified problems with how the original study was designed, analyzed and reported. They concluded that those shortcomings made it less likely the study would detect harmful neurological effects.

The findings suggest that chlorpyrifos may alter the developing brain even at lower exposure levels that do not cause obvious or immediate signs of pesticide poisoning.

Pesticide Parkinson’s Disease Claims

While the research does not establish that chlorpyrifos caused Parkinson’s disease in every person who encountered the pesticide, the findings provide support for claims that repeated exposure may damage the nervous system and contribute to the development of the disease years or decades later.

Chlorpyrifos lawsuits are being investigated for individuals diagnosed with Parkinson’s disease who experienced repeated or direct exposure to the pesticide. Potential claims may involve individuals who:

• Personally mixed, loaded or applied a known chlorpyrifos insecticide on at least five occasions
• Lived in or were present inside a home where chlorpyrifos was sprayed for termites or general pest control
• Experienced repeated pesticide drift while living or working on or near a farm
• Encountered chlorpyrifos while working at construction sites where soil, foundations or building perimeters were treated
• Experienced repeated exposure while working on golf courses, landscaping crews or other treated grounds
• Served in the military during the First Gulf War between 1990 and 1992, when chlorpyrifos was used for insect control around camps and facilities

A lawyer can help you review the products involved, the frequency and duration of exposure, the location where it occurred and the individual’s medical history to determine whether you may be entitled to pursue compensation through a chlorpyrifos lawsuit settlement.

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