Paraquat (trivial name; /ˈpærəkwɒt/), or N,N′-dimethyl-4,4′-bipyridinium dichloride (systematic name), also known as methyl viologen, is a toxic organic compound with the chemical formula [(C6H7N)2]Cl2.

This chemical is then dimethylated with chloromethane (its discoverers Austrian chemist Hugo Weidel and his student M. Russo used iodomethane) to give the final product as the dichloride salt.

[10] Although first synthesized by Weidel and Russo in 1882,[10] paraquat's herbicidal properties were not recognized until 1955 in the Imperial Chemical Industries (ICI) laboratories at Jealott's Hill, Berkshire, England.

The key characteristics that distinguish it from other agents used in plant protection products are: These properties led to paraquat being used in the development of no-till farming.

[22] There is an ongoing international campaign for a global ban, but the cheap and popular paraquat continues to be unrestricted in most developing countries.

[24] A small group of countries, including India and Guatemala and supported by manufacturers, have since blocked the listing of paraquat as a hazardous chemical for the purposes of the Rotterdam Convention.

[25] In Australia, paraquat is used as a herbicide to control annual grasses, broadleaf weeds and ryegrass in crops of Chickpeas, Faba beans, field peas, lupins, lentils and vetch.

Paraquat, with its distinctive mode of action, is one of few chemical options that can be used to prevent and mitigate problems with weeds that have become resistant to the very widely used non-selective herbicide glyphosate.

Although twice as expensive as using a single glyphosate spray, the "Double Knock" system is widely relied upon by farmers as a resistance management strategy.

[40] It is also unknown if adding glucocorticoid with cyclophosphamide to the standard care has unwanted side effects such as increasing the risk of infection.

The oxidative stress may result in mitochondrial toxicity and the induction of apoptosis and lipid peroxidation which may be responsible for the organ damage.

[46] It has been reported that a small dose, even if removed from the stomach or spat out, can still cause death from fibrous tissue developing in the lungs, leading to asphyxiation.

[49] Following Mexican efforts to eradicate marijuana and poppy fields in 1975, the United States government helped by sending helicopters and other technological assistance.

Helicopters were used to spray the herbicides paraquat and 2,4-D on the fields; marijuana contaminated with these substances began to show up in US markets, leading to debate about the program.

"[52] In a study by Imperial Chemical Industries, rats that inhaled paraquat showed development of squamous metaplasia in their respiratory tracts after a couple of weeks.

The U.S. Public Health Service stated that "this study should not be used to calculate the safe inhalation dose of paraquat in humans.

When a 2011 South Korean law completely banned paraquat in the country, death by pesticide plummeted 46%, contributing to the decrease of the overall suicide rate.

In 2022, a 22-year-old woman in Kerala, India, was convicted of using paraquat to fatally poison her boyfriend, Sharon Raj, in an attempt to end their relationship.

[58] According to the WHO (2022), some of the measures to prevent Parkinson's disease include "banning of pesticides (e.g., paraquat and chlorpyrifos) and chemicals (e.g., trichloroethylene) which have been linked to PD and develop safer alternatives as per WHO guidance" and "accelerate action to reduce levels of and exposure to air pollution, an important risk factor for PD".

In the US, a class action lawsuit against Syngenta is ongoing; the company rejects the claims but has paid £187.5 million into a settlement fund.

[66] As of August 2024, more than 5,700 cases against Syngenta (manufacturer of Gramoxone) and Chevron (the former distributor) are pending in the paraquat multidistrict litigation in the US; the first of 10 bellwether trials will start in 2024.

[67][68][69] In August 2024, the British Columbia Supreme Court certified a class-action lawsuit against Syngenta on behalf of at least two plaintiffs who were diagnosed with Parkinson's after exposure to paraquat.

For example, using protective gloves and other hygiene practices reduced the risk of Parkinson's disease among farmers using paraquat, permethrin, and trifluralin.