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Monkeys Pave the Way for Male Birth Control

Researchers found the non-hormonal contraceptive Vasalgel to be effective in preventing conception among monkeys during a trial that lasted over one year.
Photo by Cameron Zegers via Stocksy

According to a study published today in the journal Basic and Clinical Andrology, we are now one step closer to offering men a new form of birth control. During a trial period that lasted more than a year, the non-hormonal contraceptive Vasalgel was found to be effective in preventing conception among monkeys at the California National Primate Research Center.

Vasalgel has been in the works since 2010 and is intended to be less invasive and more easily reversible than a vasectomy. The gel-like contraceptive is injected into a male's vas deferens (the tube that carries sperm down from the testes) and serves as a barrier to block the release of sperm. While fluid can pass through the gel, sperm cannot, and thus are reabsorbed into the body. Previous studies have shown Vasalgel to be effective in rabbits, both in stopping sperm flow and reversing the process and reopening the vas deferens.


In the current study, researchers injected Vasalgel into 16 adult male rhesus monkeys. After a week of recovery, the primates were each reintroduced into outdoor housing that included three to nine breeding females, all with a successful reproductive history. The monkeys were kept together for at least one breeding season, which lasted approximately from mid-September to mid-May.

"The expected pregnancy rate for sexually mature females in 'corn crib' style housing is approximately 80 percent per breeding season, from unpublished data kept for colony management purposes over the past 40 years," the study states. However, by the end of the trial period, no pregnancies in the females were reported, despite the fact that researchers observed normal breeding behavior for all the study males.

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Linda Brent is the executive director of the Parsemus Foundation, the nonprofit medical research organization that funded the study. She says the results of this trial provide "confidence for real world use of the contraceptive."

"It confirms that Vasalgel works well in monkeys, which are much more similar to humans," she tells Broadly. "Additionally, this study was in a semi-natural setting and used pregnancy (or lack thereof) as the outcome, rather than measuring sperm in semen."

While two complications were observed in the trial—incorrect placement of the gel and a sperm granuloma—Brent says overall the outcome is positive. "Sperm granulomas are common after vasectomy in men, and result from tiny amounts of sperm leaking from the vas deferens into the surrounding tissue," she explains. "The incidence rate in our study was much lower than that observed in this same colony for monkeys receiving a vasectomy. So, we are very pleased that the research proved that Vasalgel was well-tolerated with reduced complications."

With the publication of this research, the next step to getting Vasalgel into the hands of men around the world is a clinical trial for humans, Brent says. "Since men currently have very few methods available (condoms, vasectomy), providing a long-acting, non-hormonal and potentially reversible male contraceptive like Vasalgel has the potential to change family planning patterns," she noted, "and hopefully, reduce the unintended pregnancy rate."

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Last year, Aaron Hamlin, executive director of the Male Contraception Initiative, called Vasalgel "a total game changer" for men and women. While condoms will remain an important tool in preventing STIs and unwanted pregnancy, he wrote for The Telegraph, they just aren't as effective as they're designed to be because of user error. This potential option "moves the contraceptive burden into shared territory," he said.