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Existing options for male contraception are condoms, vasectomy or abstinence.
So the job of preventing unwanted pregnancies often falls to women, who can take daily birth control pills, have an IUD implanted, wear vaginal rings, use a diaphragm — or when all else fails, take the morning-after pill. .
Scientists are making progress on more options for sperm producers. An article published on February 14 in the journal Nature Communication, presents a novel approach to male contraception that shows promise in mice. Researchers have tested a compound that blocks an enzyme sperm need to swim, suggesting a pathway to a temporary, fast-acting form of birth control. (Although tested in mice, many species, including human males, have the same enzyme.)
“Our lab has found the switch that activates sperm movement,” says Jochen Buck, pharmacologist at Weill Cornell Medicine and co-author of the paper, “And we’ve now developed a compound that inhibits it.”
The compound’s potential value as a male contraceptive was discovered on a whim. Five years ago, a graduate student in Buck’s lab wanted to test it on mice as a possible treatment for an eye disorder. But the student was afraid of mice so she asked another post-doc, Mélanie Balbach, for help. Balbach agreed, on the condition that she could also check what happened to the male mice’s sperm, as she knew the drug was acting on an enzyme linked to male fertility.
Balbach presented the results to Buck and lab co-director Lonny Levin at a lab meeting the following week. They were mind-blowing: After the male mice were injected with the compound, their sperm did not move.
“Lonny’s reaction was, ‘Wow! That means we could develop a male contraceptive,'” Buck recalled, “And my reaction was, ‘Lonny, that’s even better. We can have a male contraceptive in Requirement.'”
The drug stopped the sperm from swimming, slowing their rapidly beating tail into a contraction. In humans, this could mean that they would never exit the vaginal canal past the cervix into the womb. Further research showed that it was fast acting, taking around fifteen minutes to have an effect. And it was temporary – it stayed in the system for several hours.
During these hours, the male and female mice in the study had a lot of sex. Within 2.5 hours of getting the drug, it was 100% effective in preventing pregnancy. In 3.5 hours, it was 91% effective.
Buck has high hopes that it will work the same way in humans. “The prediction is, after half an hour or after five hours or after eight hours, [their] the sperm aren’t moving – and a day later, two days later they’re back to normal,” he says.
Experts unaffiliated with the study find it promising, but warn that drugs that work in mice don’t always work in humans.
“It’s very early days,” says Dr. Michael Eisenberg, urologist and director of the male reproductive medicine and surgery program at Stanford Medicine. “The idea of an on-demand pill that could potentially impair fertility is exciting, but every time a study is done in mice, you have to repeat it and make sure it’s valid in humans as well. .”
Dr John Amory, a professor of medicine at the University of Washington who is currently studying a form of male hormonal contraception in human subjects, said the new compound was a “great idea”.
“It’s an open question how well this approach would translate from mice to humans,” he adds. “There are differences in reproductive physiology between species, but it’s worth testing.”
The drug targets an enzyme in sperm that is the same in many mammals. Researchers are now trying it on rabbits and aim to start human trials in two to three years.
The demand for male contraceptives is there, says Eisenberg. “There is no doubt that there is a great need. When you look at the surveys of men, especially young men, many of them are very interested in having [more] possibilities.”
Some other experimental concepts, like hormone pills, gels and injections for men, can take weeks to start working. Some can cause mood swings, affect alcohol tolerance, or shrink the testicles. Since male contraceptives are intended for healthy men, “the tolerance for side effects is going to be very, very low,” Eisenberg says, “[The gains] need to be fairly accurate without a lot of those off-target effects.”
The side effects of this potential new treatment in men aren’t yet known, but having a male contraceptive treatment that can be taken as needed can reduce those risks, Amory says. Unlike some hormonal approaches, which must be taken daily, “you would only take it episodically, so you worry less about chronic toxicities.”
According to the researchers, the study subjects did well. “Look, our mice would never have sex if they were in pain,” Buck says. If all goes well, he says, he hopes the drug will be available in eight years.
Is it realistic? Maybe. “The joke in the field is this: A male contraceptive has been 5 to 10 years away in the last 40 years,” Amory says. “It’s always just around the corner.” Technology continues to advance, he says, and eventually society will get there.