Seemingly every year, we learn about how research is progressing toward creating alternative forms of reversible contraception for men that include pills, shots, or other devices. Despite the flurry of excitement these news pieces generate, it seems we are still quite far from mass-marketed male birth control. This month’s advance—a trial that successfully rendered mice temporarily infertile—is cut from the same cloth: It is a valid proof of concept, but likely quite a few years away from being realistically accessible on pharmacy shelves.
The new study, published in the journal Science, showed that researchers in Japan were able to block a specific protein necessary in the production of sperm—and more importantly for human men seeking a non-permanent contraception, it showed that normal sperm production resumed soon after the mice were taken off the drugs.
Specifically, scientists were examining a protein called calcineurin, which they have long suspected was instrumental in male fertility. To test this part of their theory, they genetically engineered mice that could not fully produce calcineurin and found, as suspected, these mice were infertile because the sperm they produced were not flexible enough to fertilize eggs.
Once they had tested that hypothesis, they moved on to trying to block the calcineurin in normal mice. They did this using two existing drugs—the antibiotic cyclosporine and tacrolimus, an anti-rejection drug given to patients who have had organ transplants. (Interestingly, infertility in humans is not listed as a side effect for either medication.) Within four to five days of receiving the drugs, the mice became unable to impregnate their female companions. And, within a week of being taken off the drugs, fertility returned.
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As reported by HealthDay, researcher Masahito Ikawa of Osaka University said, “It is important that we find an effective and reversible contraceptive option to allow men more control over their own reproductive futures. … The findings of this study may be a key step to giving men that control.”
Others agree that these results are exciting. Patricia Morris, director of biomedical research at the Population Council, said that this was an interesting approach because it did not involve hormones. She told Live Science, “Approaches to male contraception that target hormones can affect sex drive and thus are less desirable as contraceptives.” She added that this approach was exciting because it was so specific—targeting just one protein—and therefore, less likely to have side effects elsewhere in the body.
But in some ways this study is just a proof of concept. The researchers aren’t suggesting that the two drugs they used in mice be used in men for contraception, because both suppress the immune system, leaving a person more at risk for illness and infection. Both drugs also increase the risk of lymphoma and skin cancer. So before these findings can be translated into a monthly birth control pack for guys, researchers must first see if the effects of blocking calcineurin are the same in humans—findings in mice are often replicated in humans, but not always. Then they have to find a less toxic way to block the protein.
As Rewire has reported, there are many other attempts under way to create and perfect male birth control. For example, last year, scientists were able to render three baboons infertile by using something called Vasalgel, which is injected into the vas deferens and blocks sperm from coming out during ejaculation. This is same principle used for a vasectomy, but that procedure is permanent and severs the vas deferens. Vasalgel, which is currently undergoing testing, is intended to be reversible. It can be flushed out of the vas deferens with a second injection if a man decides he wants to be fertile again. A similar product called RISUG (reversible inhibition of sperm under guidance) is being developed in India.
As scientists continue their quest to find a new male birth control method, it remains unclear how excited most men are for these products. A survey reported in U.S. News and World Report found that 66 percent of men might be interested in a pill, 44 percent might try a shot, and 36 percent were interested in an implant.
Of course, such surveys are based mostly on hypotheticals for now. The men surveyed, for example, might not have known that some of the shots in development are intended to be administered directly into the testicles, which may have affected their reactions. And regardless, it will be many more years of studies on primates, mice, and men before anyone we know will really have to decide whether that’s something he’s willing to undergo in order to take control of his own fertility.