This story is part of a week-long series on reproduction, from prenatal testing to childfree Reddit.

On a recent morning in Los Angeles, Michael Medrano dabbed a teaspoon-sized glob of cold gel onto his shoulders. It’s just another part of his routine these days: Brush teeth, apply deodorant, comb hair, dab gel.

The gel, which Medrano describes as having the consistency of hand sanitizer, contains testosterone and progestin, a hormonal composite that suppress his body’s natural production of sperm. Massaged into his skin, it functions as the only birth control he and his wife, Julia, will use for the next year and a half.

A few years ago, Julia stopped taking Depo-Provera, an injectable form of hormonal birth control, which had caused her weight to fluctuate and made her, in Medrano’s words, “kind of moody.” Condoms worked fine, but Julia worried about slipping up. So when Medrano came across a post on Reddit recruiting participants for a clinical trial of this new kind of male contraceptive, it seemed worth a shot. Julia, happy to be relieved of the burden of managing the couple’s birth control, agreed.

Recently, some 400 other couples in nine cities worldwide have similarly worked the gel into their daily routines. It is one of the largest investigations into hormonal male contraception ever. Like Medrano, they’ll use the gel in place of other contraceptives while researchers monitor their sperm counts and any unforeseen side effects. If the gel makes it to market, it will become the first hormonal contraceptive for men—more than a half-century after the first birth control pill was approved for women.

That’s a big “if,” and it hinges on a tangle of scientific, social, and bureaucratic complications. The gel itself is more than a decade in the making, developed by researchers at the Los Angeles Biomedical Research Institute and the University of Washington. The groups have spent their careers chasing better birth control options for men, but none has made it onto pharmacy shelves yet. But the gel—called NES/T—looks very promising. Now the researchers just need to study how it works with Medrano and the other couples in the wild, hoping to prove that hormonal male birth control finally deserves to move out of the lab and into men’s lives.

The path to hormonal male contraception begins in 1957, in the laboratory of Gregory Pincus, an endocrinologist who made his name studying the effects of hormones on ailments like heart disease and schizophrenia. In 1951, encouraged by a friendship from the feminist activist Margaret Sanger—and a small grant from the Planned Parenthood Federation of America—Pincus began researching how hormones could manipulate a woman’s menstrual cycle and forestall ovulation. A combination of estrogen and progestin, he found, did the trick. His invention, called Envoid, was marketed as a “menstrual regulator with a side effect of preventing pregnancy.” In 1960, the FDA approved its use as a contraceptive, which would soon become known simply as “the pill.”

While doing the research that led to the pill, Pincus also hoped to create an analog of the drug for men. It seemed that, just as progestin could upset a woman’s natural cycle, it could also disrupt the natural production of sperm. He and other researchers put this hypothesis to the test in the late ’50s, injecting both men and women in Massachusetts mental hospitals with doses of the drug (ethical standards were looser at the time) to see if it could render men temporarily sterile. The results were inconclusive.

Arielle Pardes covers personal technology, social media, and culture for WIRED.

“As soon as this began, the women who were funding the project—[Margaret] Sanger and [birth-control pioneer Katharine] McCormick, became furious. They just wanted it for women,” says Jonathan Eig, the author of The Birth of the Pill. “It’s brilliant design if what you’re trying to do is put control into the hands of women. But over time, one of the side effects is that men are not even participating in the conversation.”