With the Supreme Court’s decision to overturn Roe v. Wade severely curtailing women’s reproductive rights, it might seem an odd moment to report good news about male birth control. Nevertheless, researchers recently announced that male birth control trials with mice were wildly successful—99 percent effective at preventing pregnancy.

Depending on the result of human trials, the drug could soon be the first effective form of birth control for those with testes apart from condoms or vasectomies. Why has it taken so long?