The purpose of the current trial is to assess the gel’s safety and longevity, not how well it prevents pregnancy. Participants were asked to use a back-up form of birth control while being enrolled in the trial.
The gel is designed to dissolve at the end of its lifetime, so the men will be followed for two years to determine how long it takes for that to happen. Eisenfrats says the goal is to have a product that lasts one to two years.
But men might want to restore their fertility before that time frame, so Contraline wants to show that it can safely reverse the procedure. The company has tested the reversibility of the gel in dogs, showing that sperm counts and sperm quality rebounded after removing the gel. It plans to launch a second trial this year to test the on-demand reversibility in people. Only men who said they do not want to have children were included in the initial trial.
While the study is small, Heather Vahdat, executive director of the Male Contraceptive Initiative, a nonprofit based in North Carolina, is encouraged by the safety profile so far. Her organization funds research into nonhormonal male birth control and has contributed funding to Contraline. “Reversibility seems very feasible,” she says.
The nonprofit Parsemus Foundation has been researching a similar gel, called Vasalgel, for several years, but has faced delays getting it to human trials. The San Francisco-based health organization partnered with a biotech company, NEXT Life Sciences, in 2022 to further develop Vasalgel. In a 2017 paper, researchers with the foundation showed that Vasalgel could be flushed out in rabbits with an injection of baking soda. Sperm flow returned in the animals after reversal.
“These are not complex components in these polymers. They’re pretty well characterized, and we know how they behave,” Vahdat says.
But any medical procedure could cause side effects or complications. Raevti Bole, a urologist specializing in men’s health at the Cleveland Clinic who’s not involved in the trial, says an injection into the vas deferens could come with a risk of skin infection, mild discomfort, or minor bruising, she says.
And there are still unknowns about the gel itself. While hydrogels are biocompatible and generally safe, Bole says she would want to know if Contraline’s product could cause permanent scarring or changes to the vas deferens and whether repeat injections could be done safely.