Birth control for rats? Don't laugh, it's a reality, and cities want it. ContraPest works by using a chemical known as 4-vinylcyclohexene diepoxide, or VCD, to destroy female rats' ovarian follicles in their most immature form, each of which contains one egg. The destruction of ovarian follicles is itself a natural process that occurs over time in all female mammals, but VCD accelerates it. VCD will impair sperm production in male rats, but it's reversible. It is nontoxic and painless.