Researchers at Weill Cornell Medicine have devised a drug that temporarily renders sperm immobile, thereby preventing pregnancy. The catch? So far, they’ve only done it in mice. But if they can translate the finding into a treatment for humans — and that’s still a distant goal — it could mean men could pop a pill and enjoy a few carefree hours, maybe even a weekend, during which they are safeguarded from creating unwanted pregnancies.

Think of it as Viagra, but for birth control.

That would be an important step forward in a field that has received too little innovation. Men have long had only two options: condoms or a vasectomy. That’s left women to carry too much of the burden when it comes to preventing pregnancy. And that burden has become heavier as more states ban abortion care and make it harder to access some forms of contraceptives.

For decades, male contraceptive research was all about keeping sperm from being made. That’s a tall order. Every day, men make tens of millions of sperm; to prevent a pregnancy, a drug needs to get that number down to less than 1 million.

Hormones like testosterone can do that, but they come with a lot of downsides. Because sperm take around 60 days to fully develop, a hormonal drug given today won’t prevent a pregnancy today, or even tomorrow — it’ll prevent a pregnancy two months from now. And reversing the drug’s effects also is a two-month process. Hormonal therapies also carry side effects like mood changes, acne, or weight gain that might be a turn-off for long-term use. (The female contraceptive pill can have similar downsides, as well as a risk of blood clots, which is one reason to invest in other approaches.)

More recent approaches, including the one taken by the Weill Cornell team, take a different tack: prevent sperm from swimming. But to reach sperm where it’s made (in the testes), a drug needs to be delivered throughout the whole body. That creates plenty of opportunities for unpleasant or even dangerous side effects.

The findings announced today suggest it’s possible. The drug blocks a protein called soluble adenylyl cyclase (or, as the researchers are calling it, “sAC”) that is critical for sperm motility. Under a microscope, the drugged swimmers look like they’re floating along, the tail of each sperm no longer furiously wagging. The effect kicked in within 30 minutes after taking the drug and lasted for over two hours. In the study, none of the mice given the drug got their mates pregnant in that 2-hour window, whereas the mice who didn’t receive it impregnated 30% of their mates.

There are, of course, the usual cautions for preliminary data. For example, researchers still need to tinker with the drug to turn it into something suitable for human testing, finessing properties like how long it can last in the body.

Even with the caveats, researchers who have spent their careers working on male contraceptives are excited about the data. “This is great!” John Amory, a researcher at the University of Washington School of Medicine, who is leading a study of one of the most advanced male contraceptives, a hormonal gel, told me after reviewing the Weill Cornell paper. “When do we test it in men?”

Not soon. But the Weill Cornell researchers do have enough confidence to have started a company, Sacyl Pharmaceuticals. Their next steps are to test their compounds in rabbits, which apparently are a good proxy for human reproduction, and to work on finding a drug with better properties — for example, one that takes effect just as fast, but works for a day or two rather than just a few hours.

The problem is that even if the science comes through, men might not be popping birth control pills any time soon.

One barrier is a lack of funding. Big pharma companies had always given the field little attention, and in the mid-aughts abandoned it altogether. Currently, the National Institutes of Health and The Bill & Melinda Gates Foundation pick up the tab for almost all the early-stage studies of male contraceptives. But government and philanthropic funding can only carry a project so far. While there have been small signs of life from industry in the broader field of reproductive health, much more momentum is needed if there’s hope of male contraceptives ever making it to market.

Another challenge, one that surely is keeping industry on the sidelines, is the still-murky regulatory path for these drugs. Researchers aren’t sure what the Food and Drug Administration will need to see to be convinced their treatments are effective. When considering approving new contraceptives for women, the agency has typically required companies to collect data across 20,000 menstrual cycles. But whether that same metric makes sense for a male contraceptive, which tends to be tested by recruiting people in committed relationships and following whether or not a partner becomes pregnant, is uncertain, says Daniel S. Johnston, chief of the NIH’s Contraception Research Branch.  

A male contraceptive will also need to be proven safe, something that will be tricky for male contraceptives because of the way regulators balance risks and benefits of new drugs. For women’s birth control methods, regulators compare the risks of a contraceptive to those of a pregnancy. Compared to birthing a child, the side effects of hormonal pills or an IUD are relatively small.

But men aren’t the ones getting pregnant. So if regulators see creating an unwanted pregnancy as “no risk” for men, even minor side effects might be seen as too risky. Men’s health researchers say that threshold needs to be reconsidered. “There is a degree of a double standard that limits the acceptance of a male contraceptive,” says Bobby Najari, director of male infertility at New York University’s School of Medicine.

An on-demand pill might ease some of those worries, since any side effects would be fleeting. “We give a lot of men Viagra and Cialis so they can have sex, and those medicines have side effects, but they wear off — and the user gets to decide if they’re worth it,” says Amory, the scientist working on the male contraceptive gel.

But perhaps the most fundamental concern for the field: If male contraceptives finally make it to market, will men actually take them? There’s at least some good news on that front. The limited available data suggest that yes, they will.

In a study conducted on behalf of the Gates Foundation and the Male Contraceptive Initiative and presented last year to the World Health Organization, about 39% of the 3,000 men surveyed said they’d try a male contraceptive within the first year it was available, and 78% would give it a shot within the first five years it was on the market. (The survey also gauged the attitudes of women and found high levels of trust in their partners to be responsible for family planning.) The results also suggest men would appreciate having a range of options — the way that women can choose between, say, a daily pill, a monthly vaginal ring, or a years-long intrauterine device.

Getting to a point where men and their female partners both have a range of options would be a welcome change. Now we just need pharma companies to get off the sidelines.

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Lisa Jarvis is a Bloomberg Opinion columnist covering biotech, health care and the pharmaceutical industry. Previously, she was executive editor of Chemical & Engineering News.

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