For three weeks, male mice in Paula Cohen's laboratory at Cornell University produced no sperm at all. Six weeks after the treatment stopped, they became fathers, and their babies were completely healthy.
This simple result comes from six years of research published in April 2026. Cohen's team believes they may have finally solved a major problem in medicine: creating a male contraceptive that is not a condom, not surgery, and not a hormone.
For decades, men have had only two choices: condoms or vasectomy. Hormonal approaches have worked well for women but have repeatedly failed in male trials. Cohen's team tried a completely different approach.
They targeted meiosis, the cell division process that creates sperm. The researchers deliberately affected only the middle stage of this process. This was important because it protected the stem cells. If those cells were damaged, a man would never become fertile again.
The compound they used is called JQ1. It was originally developed to study cancer, but it disrupts sperm production. When mice took the drug, sperm production stopped completely. When they stopped taking it, sperm production returned, and the mice could have healthy babies.
However, JQ1 itself causes neurological problems, so it cannot be used in humans. The Cornell team is using their research to find safer alternatives. They have already identified three other gene targets that could work. Within two years, they plan to create a company to develop better compounds. A human contraceptive could eventually take the form of a quarterly injection or a wearable patch.
The journey from mouse research to approved human medicine typically takes ten to fifteen years. For reproductive medicine, this is an exciting development.