A pill that can stop sperm from swimming: Is male birth control possible?

It could revolutionise male contraception. Scientists have devised a pill that makes the sperm temporarily immobile, meaning it can prevent a pregnancy. However, there is a caveat. Like many drugs, it has only been tested on mice so far. But if the findings can be translated into treatment for humans, men could pop a pill before sex and couples can say goodbye to unwanted pregnancies. It could be an alternative to condoms, which have a failure rate of 18 per cent, and vasectomies in the future. An article in Bloomberg says, “Think of it as Viagra, but for birth control.”

Devised by researchers at New York’s Weill Cornell Medicine, the “on-demand” therapy curbs the sperm from being able to swim. The experiment in mice found that the compound stops sperm cells in their tracks, preventing them from reaching the egg. However, a lot more tests are required; they will first be conducted on rabbits before humans.

If the research succeeds, men could take the pill an hour before sex and it will keep the sperm stunned for 24 hours. “This is, in the male contraceptive field, totally revolutionary,” Professor Jochen Buck at Cornell University in New York was quoted as saying by New Scientist. Most other prospective male contraceptives in clinical development are only effective after eight to 12 weeks, he says.

The pill is non-hormonal unlike contraceptive pills available for women. It will not affect testosterone or cause any side effects in men. Scientists say that they are targeting the “sperm-swim” switch – an enzyme called soluble adenylyl cyclase (sAC), which causes the cells to swim. The drug temporarily disables the sAC.

The early study on mice funded by the US National Institutes of Health was published in the journal Nature Communications on 14 February. It found that a single dose of the drug, TDI-11861, immobilised sperm before, during and after mating, reports the BBC. The contraceptive was 100 per cent effective in preventing pregnancy in mice for about two hours. The full fertility returned after 24 hours. “Our inhibitor works within 30 minutes to an hour,” Dr Melanie Balbach, lead author of the study said.

“Every other experimental hormonal or non-hormonal male contraceptive takes weeks to bring sperm count down or render them unable to fertilise eggs.” According to Balbach, the compound wore off after three hours and the males recovered their fertility. “Sperm recovered from female mice remained incapacitated. There were no side effects.” After three hours, some sperm began to swim and all recovered the next day. This means “we not only have an on-demand contraceptive but one that is also rapidly reversible,” she said.

“The team assessed the movement of sperm collected from 17 male mice, eight of whom received the drug. In samples collected 2 hours after mice received the drug, only about six per cent of sperm were mobile on average compared with about 30 per cent in samples from control mice,” reports New Scientist. “In another test, 52 male mice were paired with females 30 minutes after giving the males the drug. After two hours each pair had mated, but there were no resulting pregnancies. The drug also didn’t cause noticeable side effects, even when mice received three times the standard dose of a comparable compound continuously for 42 days,” it adds.

The sexual functioning among the mice was normal. “What I like about the proposed contraceptive in this study is the on-demand option,” Ulrike Schimpf at the KTH Royal Institute of Technology in Sweden told the publication. “It would act rapidly, temporarily and is efficient at the first dose.” Researchers will refine the drug so that it lasts longer before testing it on humans. If all goes as per the plan, the clinical trials will begin by 2025.

The drug could develop into an easy-to-use contraceptive. Men will be able to take it when they want it, and most importantly, since it has no side effects, the numbers of times they want it. While the drug stops pregnancies, it does not offer protection against sexually transmitted diseases. A condom will be needed for that.

The burden to prevent pregnancy largely falls on women. There are many options available like pills, patches and intrauterine devices. For men, there are no such alternatives. Attempt to target testosterone in the past had led to obesity, high cholesterol and depression, according to a report in the Independent.

Prof Allan Pacey, professor of andrology at the University of Sheffield, told the BBC that there was a pressing need for oral contraceptives for men, adding that the approach to knock out the enzyme in sperm critical for the movement was “really a novel idea”. “The fact that it is able to act, and be reversed, so quickly is really quite exciting… If the trials on mice can be replicated in humans with the same degree of efficacy, then this could well be the male contraceptive approach we have been looking for,” he told BBC.

According to Pacey, some tests have been done on human sperm in the laboratory and it works the same way. ‘We’re very optimistic that once men take the inhibitor, it will have the same effect… We need more [birth control] options, and men need an option so that the burden of contraception is not on females anymore,” said Balbach.