A new study in mice found an effective way to make sperm incapable of fertilizing an egg, quickly and reversibly.
The research was published Oct. 1 in the journal Science, and it looks like a promising development in the quest to develop a male contraceptive — an area in which condoms have long been the only option.
Of course, lots of studies find drugs that work great in mice but don't work in humans. And the male birth control pill has been a bit of a pipe-dream for decades — many attempts, but nothing that's made it to market.
This study, while very preliminary, suggests an interesting new approach.
Researchers treated mice with prescription drugs already on the market as immunosuppressants (used to help patients not reject transplanted organs). That's encouraging, since it means these drugs — cyclosporine-A and FK506, a.k.a. Tacrolimus — are known to be safe in humans.
In mice, the drugs made the tails of the sperm rigid, decreasing their mobility so they couldn’t penetrate the egg to fertilize it. When the scientists directly edited the mouse genetic code to make their sperm tails rigid, the same thing happened as when they gave the mice the drugs.
The drugs were fast-acting and reversible, too. They started making the mice infertile within four to five days; after the mice were taken off the drug, they were fertile again in one week.
If the researchers figure out a way to get the dosage right, one day these drugs could pave the way to a male birth control pill.
But there's reason to be cautious, especially based on what we know of these drugs in humans. Previous human studies on cyclosporine-A found that while the drug did decrease sperm motility in human sperm, men who took it at the prescribed dose were still fertile. The researchers also don't discuss in their paper the risk/benefit of a potential contraceptive that would also suppress the immune system, though it's possible they could develop new drugs that affect sperm rigidity without also acting as an immunosuppressant.
Since the current study was done in mice, many of these practical considerations are still a long way off. First, they would have to show that this approach will actually work in human men.
This study was an exciting step, but other possible male contraceptives that are in the works are further along. Some first showed promise in animals many years ago, but development has since stalled. The new study is novel, though, since it used drugs that are already FDA-approved.
Still, experts told the trade publication Endocrine Today that a male birth control pill likely won't be approved for the next five to 10 years.
An effective option couldn't come fast enough. As a 2012 review of male contraceptive methods in development so aptly quoted at the beginning of their paper:
A birth control pill for men, that's fair. It makes more sense to take the bullets out of the gun than to wear a bulletproof vest.
