ContraPest

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.

Originally designed to supplement existing rodent control strategies, is a sweet liquid that appeals to rats. However, it does not sterilize them, so a continuous supply is required. 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. The product was approved for commercial use by the U.S. Environmental Protection Agency in August 2016.

Mechanism
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. 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. ContraPest also contains triptolide, which has been reported to reduce male rat fertility. Both chemicals inhibit spermatogenesis in males and ovulation in females.

ContraPest uses oral ingestion as a major uptake method. It is appealing to rats due to its fat and salt content, which they find preferable to scavenging through trash.

Studies conducted by SenesTech demonstrated that prolonged consumption of ContraPest led to a significant decrease in rat fertility. Rats exposed to ContraPest for 50 days experienced infertility lasting up to 100 days, with reduced litter sizes in those that could reproduce.

A 2020 short-term laboratory trial with wild-caught adult black rats from Hawai'i indicated that exposure to ContraPest bait resulted in complete reproductive inhibition in wild-caught black rats for at least 15 consecutive days before mating and throughout a 43-day breeding cycle. The inhibitory effect persisted through a second breeding cycle, with partial suppression evident in a third cycle. However, fertility rebounded by the fourth cycle. It's uncertain whether the contraceptive effect affects males or females, given the treatment's impact on both sexes. Control group reproduction was not 100%, potentially due to factors like the adjustment to captivity or incomplete fertility in the source population. ContraPest did not induce permanent infertility, suggesting it's a contraceptive rather than a sterilant. Further studies are needed to assess long-term exposure effects.

Toxicity studies on ContraPest in other animals have revealed few adverse effects. The active ingredients metabolize quickly, typically within 15 minutes. Thus, if a dog or cat consumed a rat that had recently ingested ContraPest, it might experience temporary infertility as a minor side effect.

Deployment
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. Local news reported that the district was unsure of the company's early claims of success in rat control.

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

Successful trials in the New York City Subway system have suggested ContraPest's efficacy in reducing brown rat populations.

In 2024, a City Council bill in New York proposed deploying contraceptive pellets, including ContraPest, to sterilize both male and female rats in designated areas, aiming to reduce the rat population. Sponsored by Councilman Shaun Abreu, the initiative seeks to address the long-standing rat problem in the city while minimizing harm to wildlife, such as the beloved Eurasian eagle-owl, Flaco, whose death was partially attributed to rat poison.