ContraPest is a contraceptive pest control tool designed to reduce fertility in brown and black rats. It was developed by the U.S. biotechnology company SenesTech.^[1]

It is a sugary liquid, designed to be attractive to, and to be consumed by rats in order to eliminate future potential offspring. However, it does not sterilize the rats, so a continuous supply is required.^[2] The company claims that in field tests, ContraPest use caused a reduction in rat populations of roughly 40% over a period of 12 weeks or longer.^[1] The product was approved for commercial use by the U.S. Environmental Protection Agency in August 2016.^[3]

The formula was originally used by Dr. Loretta Mayer and Dr. Cheryl Dyer as part of a research program to study heart disease in post-menopausal women through menopausal mice.^[4] The active ingredient of ContraPest is the chemical 4-vinylcyclohexene diepoxide (VCD), which is a known to work when injected into peritoneal cavities of a target animal.^[2][5][6]

ContraPest uses oral ingestion as a major uptake method.^[7] ContraPest also contains triptolide, which has been reported to reduce male rat fertility. ^[1]

The city of Washington D.C. was utilizing a 5,000 unit, four-year supply of ContraPest to be used in all eight wards of the city in an attempt to combat the increasing rat population in 2020.^[8] Local news reported that the district was unsure of the company's early claims of success in rat control.^[9]

ContraPest was tested in Seattle's Queen Anne neighborhood in spring 2022 and demonstrated a 90% decrease in the rodent population within months.^[10]