Finally: The male birth-control pill?

How JQ1 works: it’s small enough to cross the blood-testis barrier, so it can reach the cells that make sperm. JQ1 targets a protein called BRDT and inhibits it, thereby preventing sperm from maturing. The result is fewer and lower-quality sperm. Using an initial, lower dose of the drug, four of seven mice that received it were able to reproduce, but their litters were smaller than normal. When the dosage was increased, none of the mice were able to reproduce at all. When the drug was stopped and mice were able to reproduce again, their litters were no different in size, activity or behavior from those of control mice.

The molecule won’t be ready for human testing anytime soon, but the researchers are hopeful for similar results. “Humans do indeed have the BRDT gene, and human genetics suggests a similar role for BRDT in sperm production,” Bradner told HealthDay. “We therefore tested activity against the human BRDT protein and found that JQ1 is a highly potent inhibitor of human BRDT.”