June 12, 2024


An emerging option for male birth control might be even more appealing to potential users than expected. Preliminary research released Sunday suggests that NES/T—a once-daily gel applied to the shoulders—can effectively suppress men’s fertility within a matter of weeks.

NES/T is short for the two main ingredients it carries, nestorone and testosterone. Nestorone, also known as segesterone acetate, is a synthetic version of progesterone, a hormone that plays a major role in regulating pregnancy and other reproductive functions. Nestorone and similar drugs are already used as hormonal birth control for women. When it’s given to men, the drug lowers the levels of hormones in the testes responsible for male fertility, including testosterone, which then leads to low sperm counts. But it also lowers testosterone circulating in the blood, which can counterproductively reduce men’s sex drive, among other adverse effects. By reintroducing synthetic testosterone through the gel, the goal is to maintain stable hormone levels in men’s blood, ensuring temporary sterility and minimizing side effects.

The gel is being developed with the help of several organizations, including the U.S. government’s National Institute of Child Health and Human Development (NICHD), part of the larger NIH. It’s now being tested in a larger-scale Phase IIB trial, which involves around 400 couples. That trial is still ongoing, but researchers have already begun to pore through some of the available data, which has provided encouraging results. In the summer of 2022, for instance, Diana Blithe, chief of the NICHD’s Contraceptive Development Program, reported that the NES/T gel’s efficacy rate so far appeared to be on par or even better than contraceptive hormonal options for women.

In this new research, presented over the weekend at ENDO 2024, Blithe and her team looked at the timing of the NES/T gel’s effectiveness. Based on other studies of hormonal birth control for men, Blithe and her team expected that most men’s sperm counts would start to be sufficiently suppressed between the 12 to 15 week mark. But they were pleasantly surprised at how much less time it took for many of their subjects.

Of the 222 participants who had their sperm checked within 15 weeks after starting treatment, 86% overall achieved suppression of their sperm counts. Within five weeks, around 20% were suppressed; by week eight, 52% were suppressed, and by week nine, 62% were suppressed. And of those who became suppressed, the median length of time it took was only eight weeks. Because Blithe’s team didn’t expect these results early on, many participants didn’t have their sperm checked between weeks four to eight. So it’s possible that the average time of suppression was even shorter than calculated.

“We’re really pleased with this result. And we think it will make the gel more attractive to people who maybe didn’t want to wait three months for it to reach its effectiveness,” Blithe told Gizmodo over the phone.

The findings are still preliminary, and it will take more time for the full Phase II data to be collected and analyzed. But Blithe and her team have been encouraged by everything they’ve seen to date. In the team’s early assessments, the gel appears to be both effective and safe, with minimal side effects for men taking it.

“I think there’s been a lot of bad publicity about hormonal methods for men that make the expectations pretty scary for folks, but that maybe works to our benefit. People enroll and realize, ‘Oh, nothing bad happened, that’s great.’” Blithe said. “We’re pretty pleased with the limited side effects that we have observed.”

Blithe and her colleagues are set to meet with the FDA next year about the steps needed to begin a larger Phase III trial and are still seeking a commercial partner to help bring the NES/T gel to the market. So it will take at least a few more years before men can potentially get their hands on the product. But for now, the future of male birth control is still looking bright.

A version of this article originally appeared on Gizmodo.



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