In June of 2019, the Office of Chemical Safety and Pollution Prevention released a memorandum on paraquat and Parkinson’s disease. In the memo, 26 studies were reviewed and ranked from high quality to low quality on the effects on humans. Another 11 were reviewed for effects in animals, and 34 for effects in tissue. For more in-depth information, read the EPA’s review of the relationship between paraquat and Parkinson’s disease.