(NEXSTAR) – The availability of a reversible form of male birth control is coming closer to fruition after researchers presented further evidence that this particular method — which suppresses the production of sperm — is safe, relatively easy and, importantly, effective.

The researchers, presenting last week at the Endocrine Society’s annual conference, shared promising results from the latest clinical trials of the NES/T method, which combines testosterone with a progestin that signals the brain to stop stimulating sperm production.

But unlike some forms or existing birth control for women, this form doesn’t come in a pill, and it isn’t administered as a shot.

It’s a gel that’s rubbed on the shoulders.

“It’s mind-blowing, how well this works,” Dr. Mitchell Creinin, of the Department of Obstetrics and Gynecology at UC Davis Health, told Nexstar. “I never thought in my career that I’d ever see a male contraceptive get this far and do this well.”

Creinin, also the director of the department’s Complex Family Planning Fellowship, has been involved with the latest trial phase of the gel’s testing (Phase 2B) at the UC Davis Health labs. He’s also worked as part of an investigative network organized by the National Institutes of Health (NIH) since its inception in the 1990s, albeit on trials of female contraceptives.

The NIH’s National Institute of Child Health and Human Development (NICHD), too, is also behind the development of this NES/T method, with Creinin working as part of a clinical trial team overseen by Dr. Diana Blithe, the chief of the NIH’s Contraceptive Development Program.

The eventual widespread availability of this new male birth control, Creinin said, could be akin to the introduction of the birth control pill in 1960.

“Men are going to want to be part of this process more, in preventing pregnancy,” Creinin believes.

The transdermal gel was developed using Nestorone®, a brand name for the progestin developed at the labs of the Population Council, a non-government research organization dedicated to reproductive and related health issues. The Nestorone blocks the pituitary hormones that regulate sperm production — but it also decreases the “intratesticular levels of testosterone” in patients, Dr. Regine Sitruk-Ware, a reproductive endocrinologist with the Population Council, told Nexstar. That’s why the gel combines Nestorone with testosterone, the latter being included to bring testosterone levels back into a normal range.

Specifically, the doses of NES/T gel involved in the latest trials (5 milliliters) contain 8 milligrams of Nestorone and 74 milligrams of testosterone, according to Sitruk-Ware. With this combination, the “vast majority” of the study’s subjects saw decreased sperm production — to “zero” in most cases, Creinin said — within four to 12 weeks of starting the gel, researchers at UC Davis Health observed. (Times varied depending on how quickly the male subject depleted the reserves of sperm already produced and stored in the body, Creinin explained.)

The gel also offers a few other benefits that current male contraceptives don’t.

“The condom has a very high rate of failure when it’s not properly used, and it interferes with the act. It’s not an ideal method,” Sitruk-Ware said. “[And] a vasectomy is irreversible.”

Rubbing a gel on the shoulders instead, Creinin added, is only about as inconvenient as brushing your teeth once a day.

“We didn’t have anybody drop out because they said it was too tough, or a problem,” Creinin said of the study participants, who were instructed to rub the NES/T dose on dry skin, on the front of the shoulders, and allow it to dry for two minutes. For the gel to work, they also couldn’t wash it off for four hours, and were instructed to wipe it off if they planned to come into contact with another person’s skin (e.g., during sex).

“Once you’re on this, you don’t have to be as strict as women do,” Creinin said, explaining that a user could “shift to the night” if they planned to hit the beach one morning, or otherwise couldn’t keep their skin dry for four hours after application.

“There’s enough hormone in there that it lasts for a good [while]. You don’t withdraw right away.”

It doesn’t necessarily need to be rubbed on the shoulders, either. That’s just what the study’s participants were instructed to do, for consistency among the trial subjects.

“It can be anywhere,” Creinin said. “We had some men, they had a little dry skin, we had them move it to their belly.”

But that raises the question: Why a gel? Could it not be a pill?

“Nestorone is a great progestin with very minimal side effects. It doesn’t work orally,” explained Creinin.

Researchers in 2016 had also experimented (and saw some success) with an injectable contraceptive for men, though the gel method appears to have fewer serious side effects — such as mood swings, more frequent urination, changes in skin or hair, according to UC Davis Health — that occur in a small percentage or users.

“They’re relatively minor, and on par or less than women have with an oral contraceptive,” Creinin said.

Also like reversible methods of birth control for women, discontinuing use of the gel returns the users to a more fertile state. Sperm counts usually get back to normal ranges in about three to six months.

“My guess is, when it’s in common use, it’ll probably be as effective as a birth control pill,” Creinin said.

Sitruk-Ware said the Population Council is already seeing evidence of increased interest in a male birth control method, especially in “the post-Dobbs era.”

“We need to give males more methods. They have to be able to decide on their own paternity, their own family size. And now, we have seen this evolution of men willing to share this responsibility,” she said.

Creinin too is “impressed” by the number of male participants who wanted to take part in the study.

“I really have so much more faith in men now. I think men do really want to be part of this process.”

Unfortunately, there’s still quite a way to go before a product like the NES/T gel is introduced to the market. A full Phase 3 study needs to be completed, and it won’t be cheap.

“In our collaboration with the NICHD, we are looking for partners as we do not have enough funds to continue, to conduct the Phase 3,” Sitruk-Ware said. “We would need to enroll almost three times as many couples as we had during the ongoing (Phase 2B) study.”

If all goes well, Phase 3 could begin in 2025 or 2026, and would likely last three or four years, Creinin said. After that, it could take another few years to finalize the results to submit to the FDA, and for the FDA to analyze and approve the findings.

When and if they do, Creinin said, it’ll be a game-changer for contraceptive health.

“Whatever method gets to the market first …  it’s going to help move things along, and change the way our kids grow up and think about contraception,” he said.

“There will be a shift. And it’s one that we need.”