Researchers first began work on a male birth control pill in the 1970s. Now, nearly half a century later, the concept is, perhaps, closer to becoming a reality than ever before.

Scientists at the University of Minnesota created a contraceptive pill that was proven to be 99% effective at preventing pregnancy in mice. According to Md Abdullah Al Noman, a Ph.D. candidate and one of the project’s main researchers, human trials could begin “as early as the end of this year.”

The new pill targets interactions with Vitamin A, key to sperm production and fertility. Mice that took the pill were functionally sterile after four weeks. Those same mice returned to normal levels of virility four to six weeks after treatments ended.