Women have about 10 options for birth control, including longer-term solutions like the IUD and implant and short-term strategies like the diaphragm and the vaginal ring. Yet for more than 100 years, men have had only two: the condom (with a failure rate close to 20%) and the vasectomy. However, the results of a new animal study suggest that a new form of birth control for men may be on the horizon.

In the new report, published Monday in the journal Basic and Clinical Andrology, researchers tested a new contraceptive called Vasalgel in male monkeys, and found that it was effective at preventing pregnancy during the monkeys’ mating seasons. Vasalgel consists of a polymer gel injected into the vas deferens — the tube through which sperm swims — that blocks sperm from escaping. It’s long lasting and reversible.

The study was small and not performed in humans. However, the results are intriguing. Sixteen adult male monkeys were given Vasalgel injections, and after recovering, they were returned to their usual housing with female monkeys. All the males were followed for at least one mating season, and seven of the monkeys were followed for two years. The researchers reported that there were no conceptions during the study period. ” We were impressed that this alternative worked in every single monkey, even though this was our first time trying it,” the study author Angela Colagross-Schouten, of the California National Primate Research Center, said in a statement.

The study was funded in part by Parsemus Foundation, a division of which is Revolution Contraceptives LLC, the developer of the gel.

There were a few minor complications, including one incorrect placement of the gel. But overall the researchers found that the rate of sperm-related complications in the monkeys was lower than the rate of complications among monkeys who had undergone a vasectomy.

Parsemus FoundationParsemus Foundation 

Elaine Lissner, founder of the Parsemus Foundation, says the organization is optimistic that human clinical trials of the method could begin in 2018, and that ideally the method could be safely used for at least 10 years or longer.

The researchers still need to test the reversibility of the method in monkeys, and several more safety studies need to be done before a human trial occurs. The group cites a similar product called RISUG (Reversible Inhibition of Sperm Under Guidance), which is being tested in human clinical trials in India with success, as evidence the product can work in men. The Parsemus Foundation says it plans to look for social investors to help fund the further studies.

The new study adds momentum to ongoing male birth control research. In October of 2016, a promising trial found that hormonal injections given to men were 96% effective at suppressing sperm production. Yet excitement over the results was short-lived when it was announced the trial had ended early because some men in the trial found the side effects — including mood swings and depression — untenable. Though drug companies and government research groups have worked on new forms of male contraception since the 1970s, in the past decade, the number of funders has dwindled. Yet men seem to be interested in more birth-control options: more than 80% of the men in the trial said they would use the method if it were available.

“People should not let the disappointments about hormonal methods color the great potential of nonhormonal methods,” says Lissner, citing the potential for fewer hormone-related side effects with Vasalgel.

For now, the field of male contraception remains a waiting game, though the authors believe the new study — if accompanied by further research — can move the science forward.

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