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10.03.15 4:03 AM ET

It’s Almost Here: ‘The Pill’ for Men

Japanese scientists have identified an immunosuppressant pill that could act as non-hormonal male birth control.

If you’re a man frightened by the thought of getting a shot in your vas deferens to prevent unintended pregnancies, good news: Researchers in Japan may have just identified the key to creating a birth control pill designed especially for you.

A team of scientists based out of Osaka University have published new research in Science suggesting that immunosuppressant drugs used for organ transplant patients could be used to develop a reversible oral contraceptive: a version of “the pill” for men.

Male birth control is a sticky business. Female birth control prevents ovulation through hormone regulation but male birth control must directly alter, immobilize, or block sperm cells on a physical level.

So far, some of the most promising developments in male birth control have been polymers like Vasalgel that work by preventing sperm from leaving the body in the first place. The semi-permeable gel is injected directly into the vas deferens but it can be flushed out with a second injection. This contraceptive has been successfully tested in male primates and the manufacturer is hoping to complete human trials by the end of 2015.

Potential forms of oral contraception for men, by contrast, tend to work by immobilizing the sperm or otherwise rendering them incapable of fertilization. One potential drug would function by reducing the motility of sperm with anti-eppin antibodies. The sperm would still come out in the ejaculate, as Nature noted in 2004, but they would essentially be dead on arrival.

Now, Osaka University researchers have identified another possible way to take sperm out of the running.

Microbial disease researcher Haruhiko Miyata and his team started with the knowledge that two calcineurin inhibitors—cyclosporine A and FK506 for the technically-inclined—have been known to affect the development of sperm and to impair their motility. Through research on mice, the scientists isolated a form of the protein calcineurin that is “sperm-specific,” and hypothesized that targeting this sperm calcineurin could have a contraceptive function.

From that point, their process grew more complex and involved copious mouse sex.

First, the researchers depleted the sperm-specific calcineurin in male mice. Although these mice still developed sperm, they had no success impregnating their female companions. But the scientists looked closer at their sperm and made an intriguing discovery: Although their sperm had comparatively less success reaching the ampulla—the section of the fallopian tube where fertilization occurs—some sperm were indeed reaching the finish line.

So why weren’t the female mice getting pregnant?

Subsequent tests revealed that the sperm from mice without the sperm-specific calcineurin could not successfully penetrate eggs because the midpieces of the sperm themselves were bent and rigid. Further experiments showed that these effects were not permanent. Mice who took cyclosporine A and FK506 “recovered one week after halting drug administration” and their sperm started to move and bend normally as well.

The authors are quick to point out the implications this could have for research into male birth control for humans.

“Specific inhibition of sperm calcineurin… may lead to the development of reversible and rapidly acting male contraceptives that target spermatozoa in the epididymis but leave testicular function intact,” the authors write.

In other words, everything still functions normally but the sperm just can’t cut it.

Although this research is still in its early stages, there is already speculation that a male birth control developed out of calcineurin inhibitors would have one major advantage over the female pill: it would be non-hormonal. Many of the side effects of female birth control result from its reliance on hormone regulation.

“We certainly need male contraceptives, and new designs that aren’t hormone-based are really welcomed in terms of acceptability,” Patricia Morris, Population Council director of biomedical research told LiveScience.

The lead author of the study did not immediately respond to The Daily Beast’s request for comment.