Popular Pesticide Linked to More Than Double the Risk of Parkinson’s Disease

New research has revealed a potential connection between long-term exposure to chlorpyrifos, a widely used pesticide, and an increased risk of developing Parkinson’s disease. A December 2025 study conducted by researchers at UCLA Health found that individuals with prolonged residential exposure to chlorpyrifos are more than 2.5 times more likely to develop the debilitating neurological condition. These findings may have significant implications for farmworkers, agricultural employees, and those who have lived and worked in areas where chlorpyrifos was heavily sprayed.

What is Chlorpyrifos?

Chlorpyrifos is an organophosphate insecticide that has been utilized in agriculture since the 1960s. Originally developed to combat pests in various crops, it became one of the most commonly used pesticides in the United States, sprayed on corn, cotton, strawberries, and other crops. Chlorpyrifos was also used for other purposes, such as residential pest control, structural termite treatment, and golf course maintenance. 

Following years of pressure from public health and environmental groups, most residential uses of chlorpyrifos were banned in 2000, and in 2020, Corteva Agriscience announced that it would no longer manufacture the chemical. However, existing stocks of chlorpyrifos continued to be used, and the pesticide remains available for certain agricultural applications in the U.S. today.

How Does Chlorpyrifos Work?

Chlorpyrifos works by inhibiting acetylcholinesterase, an enzyme essential for the proper functioning of the nervous system. This disruption can lead to a buildup of acetylcholine, resulting in overstimulation of nerve cells. While this mechanism is effective against pests, it may also pose significant risks to human health, particularly for those who are frequently exposed to the chemical, such as farmworkers and residents living near treated agricultural areas.

Potential Link Between Chlorpyrifos and Parkinson’s Disease

A recent UCLA Health study published in the journal Molecular Neurodegeneration provides compelling evidence linking chronic chlorpyrifos exposure to an increased risk of Parkinson’s disease. Researchers involved in the study analyzed data from nearly 1,700 individuals – 829 diagnosed with Parkinson’s disease and 824 control subjects. The results indicated that “Long-term residential exposure to [chlorpyrifos] was associated with more than a 2.5-fold increased risk of developing PD.”

Laboratory experiments conducted on mice alongside the human study revealed that chlorpyrifos damaged dopamine-producing neurons, which are critical for movement and coordination. “Mice exposed to aerosolized CPF developed motor impairment, dopaminergic neuron loss, microglial activation, and an increase in pathological α-synuclein (α-syn),” the researchers noted. 

Alleged Chlorpyrifos-Related Illnesses and Health Effects

Exposure to chlorpyrifos has been linked to a possible increased risk of various health issues, including:

• Neurological Disorders: In addition to Parkinson’s disease, chlorpyrifos exposure may contribute to other neurological conditions, such as cognitive impairments and developmental delays in children.
• Respiratory Issues: Inhalation of chlorpyrifos can lead to respiratory problems, particularly in individuals with pre-existing conditions.
• Endocrine Disruption: Some studies suggest that chlorpyrifos may interfere with hormonal systems, potentially leading to reproductive and developmental issues.

Who Faces the Greatest Risk of Chlorpyrifos Exposure?

Certain groups may face a greater risk of exposure to chlorpyrifos, including:

• Farmworkers: Those who handle, mix, and apply chlorpyrifos are at the highest risk due to direct contact and inhalation.
• Residents Near Agricultural Areas: Individuals living in close proximity to treated fields may experience exposure through airborne particles and contaminated water sources.
• Children: Young children are especially vulnerable to the neurotoxic effects of pesticides, as their developing brains are more susceptible to damage.

Chlorpyrifos Regulations in the United States

The regulatory status of chlorpyrifos has been the subject of years of debate. Although the EPA has taken steps to limit its use, legal challenges have led to changes in how the pesticide is regulated, and some agricultural uses continue today. As new research continues to emerge, the findings could also influence future legal claims brought by individuals who believe they developed Parkinson’s disease after prolonged exposure to chlorpyrifos.

The debate surrounding chlorpyrifos and Parkinson’s disease reflects broader concerns about the safety of agricultural pesticides. Paraquat, another widely used agricultural herbicide, has also come under increased scrutiny due to studies examining a possible link between long-term paraquat exposure and Parkinson’s disease. Like chlorpyrifos, paraquat has remained the focus of ongoing scientific research, regulatory review, and legal claims. 

Ongoing Research and Future Implications

The new UCLA Health study represents another step forward in understanding the potential long-term health effects of chlorpyrifos exposure. Although researchers caution that additional studies are needed, the findings add to growing scientific evidence examining a possible connection between chlorpyrifos and Parkinson’s disease.

The chlorpyrifos research may also shape future discussions about pesticide regulation in the U.S. while informing legal claims brought by individuals who allege that they developed Parkinson’s disease after years of chlorpyrifos exposure.