Does Paraquat Cause Parkinson’s Disease?

The Short Answer

People exposed to paraquat get Parkinson’s more often than people who were not. That has turned up in study after study, especially among those who worked with it for years.

That is not the same as proving paraquat caused any one person’s illness. A link in a population means two things show up together more often than chance would explain. Proving that your Parkinson’s came from your spraying is a harder question, and it is the one being fought over in court.

What Parkinson’s Disease Is

Parkinson’s is a brain disease that gets worse over time and affects how you move. Nerve cells that make dopamine, the chemical that helps control movement, are damaged and die off. The signs people notice first are a tremor, stiffness, slowed movement, and trouble with balance.

Doctors usually cannot say what caused it in any one patient. Most cases are thought to come from some mix of a person’s genes and something they were around.

What the Research Has Found

The concern comes from two directions. In the lab, paraquat kills the same dopamine-making cells that die in Parkinson’s, and its chemical shape is close to a compound already known to cause Parkinson’s-like symptoms. In people, studies comparing farm workers who were exposed with those who were not have found more Parkinson’s in the exposed group. Reviews that pool many studies point the same way.

How much more is where it gets murky. A 2019 review of nine studies put the increase at about a quarter. Other research has reported rates twice as high or more among people exposed at work. Those studies measured exposure in different ways and looked at different groups of people, which is much of why the numbers spread so far apart.

The evidence does not all run one way either. Studies differ in how they worked out who was exposed and how much, and in how they handled the other things that can bring on Parkinson’s. That is why scientists say linked to and higher risk rather than caused by, and why this is still an open field rather than a settled one.

Why Regulators Have Reached Different Conclusions

The same evidence gets read differently depending on who is reading it. Dozens of countries have banned paraquat outright. In the United States the EPA has said the data do not establish a clear causal link, while keeping tight limits on who may use it. An EPA memo in 2016 did acknowledge there is a large body of research on paraquat and Parkinson’s, without treating the question as answered.

That gap, between countries and between agencies, is a good part of why these cases are so hard-fought.

Long-Term Exposure, Not Acute Poisoning

Two very different things get mixed up here. Swallowing paraquat is an emergency: a single sip can kill an adult and there is no antidote. That is not what the Parkinson’s research is about.

The Parkinson’s question is about small amounts, over and over, across years of mixing, loading, spraying, or working near where it was sprayed. The people studied for this risk are the ones who were around it season after season.

Who Is Most Often Studied for This Risk?

• Farmers and farmworkers
• Licensed pesticide applicators
• Anyone who mixed, loaded, or sprayed herbicides
• Field hands working in or beside treated ground
• People exposed again and again over many seasons

Why This Question Is Central to Litigation

Every case turns on whether paraquat caused that particular person’s Parkinson’s, so this is the whole fight. The people suing argue the research backs the link and that the companies never warned anyone. The companies argue the science does not prove cause. How judges and experts weigh that evidence decides these cases.

The legal side, including who brings these claims and what records matter, is on the Paraquat Parkinson’s Lawsuits page. For the chemical itself, see What Is Paraquat?

This fight is not settled, and it has already changed the course of the litigation once. In 2024 a judge threw out the testimony of the plaintiffs’ main expert on causation and dismissed the first four test cases. Where that leaves things now is tracked on Paraquat Lawsuit Updates.