Scientists say they have inched closer to making a reversible male birth control a reality.
Contraception has traditionally placed more of the day-to-day burden on women, through options such as pills, implants and intrauterine devices (IUDs). While effective, some methods can bring unwanted side effects, including mood shifts, weight changes, or in rare instances, blood clots.
Now, researchers say they may be getting closer to a temporary male contraceptive that works by pausing fertility at a precise point in sperm development. The goal is a treatment that suppresses sperm production while it’s used, then allows fertility to return once it stops.
One compound drawing attention is JQ1. Scientists already knew it can interfere with BRDT, a protein involved in sperm production. New findings dig further into the mechanism—clarifying why the approach works, how recovery unfolds after stopping the drug, and which step of sperm formation may be the safest and most reliable point to target.
A major challenge in designing a male contraceptive is choosing the right stage of sperm production to disrupt. Interfering too early—at the stem cell level—raises fears about long-term or permanent fertility effects. But acting too late, once sperm are already formed, could leave enough viable sperm to still cause pregnancy.
The team closely charted how sperm recover at the molecular and genetic level, describing a path toward a reversible, non-hormonal male contraception strategy. Their work points to an intermediate window—early enough to stop healthy sperm from forming, but late enough to leave stem cells intact so the system can reboot after treatment ends.
“We’re practically the only group that’s pushing the idea that contraception targets in the testis are a feasible way to stop sperm production,” said Dr Paula Cohen, corresponding author and genetics professor in the Cornell University College of Veterinary Medicine.
To locate a safer target, the researchers focused on meiosis. This is the stage where chromosomes align, exchange genetic material, and separate—eventually producing individual sperm cells.
In the experiment, male mice received daily JQ1 injections for three weeks. JQ1 blocks BRDT, a protein that is only active during sperm development.
After the treatment period, the scientists assessed sperm count, testicle size, and whether the mice were still able to produce offspring.
They also inspected cells under a microscope and used genetic sequencing tools to identify which genes were being switched on or off.
Following three weeks of dosing, the male mice became infertile and could not impregnate females. Testicles shrank, sperm counts fell steeply, and analysis of tissue showed sperm development had halted after the earliest steps.
Cells progressed to the stage where mature sperm should form, and then stalled.
The researchers backed this up by looking at patterns of gene activity. A normal, high-activity “transcriptional burst” that occurs during a particular phase of meiosis had been effectively shut down.
Once the JQ1 injections stopped, the team waited six weeks before rechecking sperm counts, testis size, chromosome behavior, and gene activity.
At that point, broad indicators—like sperm numbers and testicle size—had largely returned to normal. The mice could also father offspring again, although the first litters were smaller than usual.
However, deeper investigation showed recovery was not fully complete. The crossover sites where chromosomes swap DNA—an essential step for producing healthy sperm—had not entirely returned to baseline.
Some sperm still appeared abnormal in shape when viewed under the microscope, and gene networks tied to sperm movement and energy remained disrupted. Those more subtle issues took far longer to resolve—around 30 weeks, or roughly seven months.
After that longer recovery period, chromosome crossovers, gene activity patterns, and sperm appearance became indistinguishable from those in untreated mice.
Although some molecular and structural markers lagged behind, the delay didn’t translate into lasting fertility issues or abnormalities in the offspring. The mice ultimately recovered, and the pups were healthy.
“Our study shows that mostly we recover normal meiosis and complete sperm function, and more importantly, that the offspring are completely normal,” Cohen said, per Science Daily.