How NES/T Gel Works, and Where Its Trial Stands in 2026

Published November 1, 2026 · Investigational · Not approved

If you ask which male contraceptive is furthest along, the answer by trial stage is NES/T, a daily gel. It was developed by the Population Council in collaboration with the U.S. National Institute of Child Health and Human Development (NICHD), and Contraline holds exclusive worldwide rights to develop and sell it, according to Contraline's June 2026 announcement. NES/T is investigational and has not been approved by the FDA or any other regulator.

What's in it

NES/T combines two hormones: segesterone acetate (brand name Nestorone), a synthetic progestin, and testosterone. Contraline says each is individually approved by the FDA for other uses, but the combination, for this purpose, is not. The gel is applied once a day to the shoulders and upper arms. In the Phase 2b study, the daily dose was 8 mg of Nestorone and 62 mg of testosterone, according to the Penn Medicine study page.

How it's designed to work

Sperm production depends on signals from the brain's pituitary gland. The progestin is meant to turn those signals down, which lowers sperm production. But it also lowers the body's own testosterone, so the gel adds testosterone back to keep levels in the normal range. In Contraline's words, it's designed "to temporarily pause sperm production while maintaining normal testosterone levels." Effects aren't immediate: the Penn study page lists a suppression phase of up to 20 weeks before couples rely on it. That's a design and trial description, not a promise of how it would work for any one person.

The Phase 2b trial

The main study is NCT03452111 on ClinicalTrials.gov, listed as completed, with a completion date of September 2024. Contraline says it enrolled 462 couples at 17 sites [1][2]. According to the Penn page, couples took part for about two years, in phases:

Screening: 4 to 8 weeks.
Suppression: up to about 20 weeks of daily gel while sperm counts drop.
Efficacy: 52 weeks using the gel as the couple's only birth control, with regular sperm checks.
Recovery: about 24 weeks after stopping, to track sperm counts coming back.

What results are public

Less than you might think. A 2024 Endocrine Society conference abstract reported that 86% of 222 evaluated participants reached the study's sperm-suppression threshold during treatment. Contraline says the trial "demonstrated encouraging efficacy, tolerability, reversibility, and user acceptability" [1], but full results, including pregnancy rates and detailed side effects, haven't been published in a peer-reviewed paper as of this writing. Until they are, we can't say how NES/T measures up against WHO's new benchmarks (see our guide to WHO's standards).

What's next: Phase 3 in 2027

Contraline raised a $92.5 million Series B in June 2026 and says it expects to start Phase 3 in 2027 [1]. CEO Kevin Eisenfrats told Fierce Pharma that the money should fund the whole Phase 3 through to an FDA submission. Even if Phase 3 starts on time and succeeds, it would take years more before any approval decision.

The open question: side effects

Because NES/T changes hormone levels, mood and libido are the side effects people watch most. An earlier injectable hormonal method was stopped in 2011 over mood effects, and a 2026 reanalysis suggests hormone levels may help explain who is affected; we cover it in our explainer on why that trial stopped. NES/T uses a different progestin and delivery route, so those results don't carry over directly. NES/T is investigational and not approved. See the status tracker for updates.

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This article is news and education, not medical advice. No male contraceptive described here is approved. Get notified of updates.