It may be possible to create male birth control by altering how sperm develop, according to new research published this week in Science. Researchers blocked a protein that plays a role in sperm production — and that was enough to render male mice temporarily infertile. Since drugs that alter this protein are already on the market, development of male birth control could happen swiftly if the method works in people too.

In the study, scientists genetically altered mice so the rodents’ reproductive cells didn’t express certain genes. This caused the male mice’s sperm to develop abnormally, preventing the sperm from fertilizing any eggs. Here’s the important part: the effect could be recreated using certain drugs.

Currently the strongest option for men is a vasectomy

Nowadays, the burden of birth control is usually placed on women, for whom many forms of hormonal birth control already exist. Currently the strongest option for men is a vasectomy, which prevents sperm from leaving the testes. This option, in addition to requiring a surgery, is mostly permanent. Condoms can be an option for men, but they can break and can also decrease sensitivity. Another product in development is called Vasalgel, which is awaiting approval by the Food and Drug Administration; it’s not permanent but does block sperm from passing through the penis for 10 years.

So an oral, reversible male contraceptive may be a much more attractive route for both men and women. It would also give couples more options to help decide which form of birth control works best for them."The development of new approaches that will enable couples to share birth control responsibilities ... has been an unmet need for a long time," said Lee Smith, chair of genetic endocrinology at the University of Edinburgh, who was not involved in the study.

This new method described in Science could help meet that need. An enzyme called calcineurin, which also plays a role in the immune system, is known to affect male fertility. Today’s finding suggests that there’s a sperm-specific version of the enzyme, found only in cells that produce the gamete, says study author Masahito Ikawa, a researcher at the Institute for Microbial Diseases at Osaka University.

The mutant sperm had rigid tails

The sperm-specific version has two crucial genes turned on. So scientists created a group of mice that didn’t have the sperm-specific enzyme, by knocking out those genes. These mutant mice were healthy, and they were able to have sex and ejaculate normally. But the male mice couldn't impregnate any of the females. Using a high-speed camera, the researchers analyzed the mice's semen; the mutant sperm had rigid tails, making it harder for them to swim. The sperm were also unable to penetrate the egg's membrane.

In a second part of the study, normal mice were treated with medication that block calcineurin; these drugs are often taken as pills to treat rheumatoid arthritis. (They’re also given to organ transplant patients to stave off rejection of the donor organ.) After four to five days of receiving the medications, the male mice became infertile. When the mice stopped receiving the drugs, they were fertile again a week later.

While these findings are promising, mice obviously aren’t people — so the research may not hold up in clinical trials. Though medication to block calcineurin is already available, these drugs aren’t designed to specifically target sperm production; the compounds would probably need to be altered to keep men healthy. But the research gives experts hope that a reversible — and less invasive — form of male birth control could be available soon. The fact that medications to block calcineurin are already on the market means the drug approval process could be relatively quick, according to Smith. "This should expedite development of a contraceptive," he said.