Paraquat is one of the world's most widely used herbicides. It is useful because it is fast-acting, nonselective, effective against some difficult weeds and relatively inexpensive.
Developed by the British chemical company Imperial Chemical Industries in the 1950s, this broad-spectrum weed killer works by disrupting photosynthesis and creating reactive molecules that rapidly destroy plant tissue. It is usually applied as a spray before planting or between crop rows.
Paraquat is also one of the most acutely toxic herbicides ever used, especially to humans and other mammals. Small ingested amounts can be fatal, and severe poisoning can occur through concentrated skin or eye exposure. Once inside the body, it targets the lungs because cells there naturally pull it in, causing severe and permanent lung damage over time. There is no specific antidote, and treatment is mainly supportive and focused on preventing absorption and managing organ damage.
The Parkinson's disease link is arguably the most prominent public controversy surrounding paraquat globally and has been a major factor in modern activism and legal bans. Thousands of lawsuits in the United States and intense debates elsewhere center on studies linking chronic, low-level occupational exposure to paraquat with a significantly increased risk of developing this incurable disease. However, regulatory agencies such as the U.S. Environmental Protection Agency (EPA) have historically debated whether the data proves direct causation.
Because paraquat is notoriously fatal in even tiny amounts and is frequently swallowed, often accidentally when transferred into beverage containers, manufacturers added a strong warning odor, a blue dye and an emetic (a chemical that induces immediate vomiting) to help prevent ingestion. Unfortunately, these measures have had only limited effectiveness in preventing fatalities from intentional or accidental swallowing.
Environmentally, paraquat binds tightly to soil particles upon contact, which prevents it from leaching into groundwater and limits its persistence. However, it can pose risks to wildlife, including birds and aquatic organisms, if it enters water supplies through spray drift or soil erosion. Unlike some other herbicides, weeds have been relatively slow to develop resistance to paraquat, although heavy reliance on it as a fallback treatment has increased resistance in several aggressive species globally.
Because of its acute toxicity, paraquat is banned or heavily restricted in many countries and, where permitted, typically has strict handling and application requirements. Significantly, nations that ban it domestically (such as the UK, Switzerland, and China) have historically been major producers and exporters to developing markets or to the U.S.
As of mid-2026, paraquat is formally banned in 74 countries, including the EU and adjacent nations. In the U.S. paraquat remains legal as a restricted-use pesticide for certified applicators, although ongoing federal health reviews and regulatory scrutiny have prompted individual states, such as California and Vermont, to weigh or enact local legislative bans and phase-outs, and massive lawsuits continue to heavily shape its legal status. Elsewhere, some national or regional bans have faced enforcement problems, and illegal or unregistered products may still circulate.
Amid escalating commercial, environmental and legal pressures, major western agrochemical giants such as Syngenta have finalized their exit from global paraquat manufacturing. Production has subsequently shifted heavily toward generic and state-backed manufacturers in countries such as China and India, keeping global supply robust for agriculture across Asia, Africa and the Americas.
However, reflecting global divisions over toxic agricultural chemicals, efforts to list paraquat as a "severely hazardous pesticide formulation" under the Rotterdam Convention have repeatedly stalled due to resistance from a small group of agricultural countries.
While agricultural lobbies frequently argue that restricting or banning inexpensive chemicals such as paraquat drives up food production costs, public health advocates and agricultural studies counter that many countries have transitioned away from it with no measurable loss in crop yields.
Alternatives that can be used in combination in place of paraquat include mechanical cultivation, mowing or hand weeding; cover crops, mulches and crop rotations; precision application and integrated weed management; herbicides with different modes of action; crop varieties and farming systems better suited to reduced chemical use.