Though the female birth control pill—which contains hormones that prevent the ovaries from releasing eggs—has been around since 1960, men have surprisingly few of their own reversible contraceptive options. 

But by injecting a compound into the abdomens of mice, the authors of a recent study were able to effectively inhibit the development of sperm without any adverse side effects.

“We’re hoping this will provide a male consumer with one of many different [birth control] options, just like women have now,” said Chuen-yan Cheng, lead author of the new study and a senior scientist at the Population Council’s Center for Biomedical Research, an international non-profit.

Research on male birth control methods has been ongoing for decades, but until recently, it was met with resistance from policy makers and consumers alike. When the idea of a hormone-based male contraceptive was first introduced, many men thought it would shut down sperm production or decrease their libidos. But men’s attitudes are different now in the age of DNA paternity testing and high child support, said Elaine Lissner, director of the San Francisco-based Male Contraception Information Project.

“It’s a basic human right to be able to decide when to have a child, and the tools that men have for doing that are not ideal,” Lissner said. “You can’t say that men aren’t willing to participate if you don’t have good choices for them.”

The choices now in development fall into two categories: hormonal methods that affect the entire body (much like the female contraceptive pill) and non-hormonal methods that physically block the production of sperm.

The hormonal methods—implants and shots that contain testosterone and progestin—are “way ahead of the non-hormonal stuff,” said John Amory, a physician and researcher at the University of Washington who is working on a contraceptive pill for men.

But the “holy grail” in male contraceptive research is finding a non-hormonal method, Lissner said.

“Hormones affect the entire body, which is why women have so many problems with the pill,” she said. “It’s taken us years to figure out what the pill is doing, and we don’t want to go through that experience again with men.” 

Cheng’s new mouse study, published in the November issue of Nature Medicine, takes a non-hormonal approach.

A few years ago, Cheng’s lab found that a molecule called Adjudin induced infertility when given orally to male mice. Adjudin works by preventing developing sperm cells from attaching to nurturing tissue in the testes. But giving Adjudin orally causes muscle atrophy and significant side effects in the liver, Cheng said. 

So in his latest experiments, Cheng sought to bypass that problem by delivering Adjudin directly to the testes. He attached Adjudin to a molecule called follicle-stimulating hormone (FSH), which only has receptors in the testes, and injected it directly into each mouse’s abdomen. 

“FSH carried Adjudin right to the testes,” Cheng said, “and lowered the side effects by many orders of magnitude.”

About two weeks after being injected with this new Adjudin-FSH compound, most of the mice lost fertility, but by 12 weeks the mice were fertile again. This reversibility is key, Cheng said, to making an effective contraceptive for humans. 

An approach that targets the testes specifically “is very appealing,” Amory said. But a repeated injection into the belly, he said, “is just not going to play” among many American men. 

Cheng admits as much and says that in the next stage of research, he hopes to make the Adjudin-FSH compound into a gel or nasal spray.

But making this compound into a gel, Amory said, is also going to be a challenge.

“This is a pretty large molecule and not going to be easily absorbed across the skin,” he said. 

Additionally, the adverse effects that Adjudin produced in earlier experiments are still worrisome, Amory said.

Citing the wave of lawsuits in the 1970s over female IUDs, Amory adds, “Contraception is a bit risky, and American companies have not been eager to get involved.”

Big Pharma might also be less interested in non-hormonal treatments because they’re less profitable than a hormonal product that must be taken monthly, Lissner said.

But neither hormonal or non-hormonal methods will be coming out anytime soon.

“We’ve been hearing that it’s 5 to 10 years away since the ‘80s,” Lissner said.

Originally published October 30, 2006

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