Most people in the United States accept the notion that it takes two to tango in bed. But ever since the birth control pill received government approval 50 years ago, women have been waiting for the other shoe to drop -- when men get a pill, patch or injection to bear the burden of birth control.
A large study published Monday in the Journal of Clinical Endocrinology and Metabolism indicates that science may be bringing us closer to a male "pill," although the idea of hormones for male birth control still stokes a heated debate among doctors.
Researchers recruited more than 1,000 Chinese men who had fathered at least one child two years before the study with their partners to receive injections of testosterone undecanoate (TU) in tea seed oil every month.
After two years, the injections had 95 percent effectiveness for preventing pregnancy overall, and about 98 percent effectiveness for men whose sperm levels dropped off at expected levels within the first few months of the trial.
Male contraceptive researcher Dr. John K. Amory was impressed by the ability of the injections to drop sperm counts.
"The goal is to try to get to 99 percent effectiveness [for pregnancy prevention]," said Amory, who is an associate professor of medicine at the University of Washington in Seattle.
"They went down to 1 million sperm in a milliliter of semen from the normal 20 to 200 million sperm per milliliter," he said.
Although testosterone usually triggers sperm production, Amory said too much testosterone can shut down the testes.
"If you give external testosterone in the blood, this decreases the testosterone in the testes," Amory said. "It's because the body has what we call a feed-back loop. The brain sees the hormones and thinks, 'Oh, we're making plenty of that,' and shuts off [sperm] production."
The authors write that more long-term studies of testosterone injections are needed for safety, but "that these promising findings provide encouragement that male hormonal-contraceptive regimens may offer a novel and workable alternative to existing family planning options."
But not everyone agrees that hormones for male birth control are novel, or a workable alternative.
Doctor's Debate About Hormones for Male Birth Control
"It's really not new and it's been abandoned for a number of reasons," said Dr. Larry Ross, past president of the American Urological Association.
The first reason, Ross said, is that testosterone injections proved to be unreliable in the past.
"Failure rates as high as 20 percent have been reported," said Ross, who is also professor of urology at the University of Illinois at Chicago.
On the other hand, Ross said testosterone injections can be too effective and, over time, can sterilize a man. "There are not an insignificant number of men who will develop permanent sterility," he said.
Ross said that while men might not see any damage from low testosterone levels in the testes in the short term -- for 6 months or a year -- any longer and the testes can begin to scar.
"Places we've seen this is in steroid abuse like weight lifters, and there's been a lot of talk about baseball players lately," Ross said.
Indeed, Ross said, discussions about testosterone injections for male birth control at urology conferences largely leave out testosterone talks these days.
But researchers of male birth control in the United States say they have to kindly disagree with the notion that the effects of abuse rule out any future for testosterone as birth control.
"I'm not sure I agree that it can lead to sterility," said Armory, who added that in the 35 male hormonal-contraception studies using testosterone he has seen, there has never been a case of irreversible sterility.
"There are these reports of sterility in bodybuilders who take hormones that we don't use; those are veterinary hormones," Armory said. "We have ongoing studies using hormones and, if the subjects were at risk for sterility, we wouldn't be able to do the study."
Armory, who recently started a birth control study with testosterone gel, said researchers are largely experimenting with the timing and application of testosterone at this point.
Would Male Birth Control Ever Work?
Dr. Ronald Swerdloff, a veteran male contraceptive researcher, believes there are issues other than safety or effectiveness that are keeping male hormone contraception research from reaching its goal.
"This as been known for 15 and 20 years that [testosterone injections] are quite effective and that there is a limitation that it didn't work on everybody," Swerdloff said.
"But there's another problem and the other problem is that it doesn't work right away," he said.
Unlike the condom, which works immediately, or the pill which works within one month's cycle, a man on testosterone may have to wait three months before sperm production shuts down.
Swerdloff thinks the lack of interest by pharmaceutical companies may be another contributor to barriers for male hormone contraception research.
"There hasn't been success in finding a pharmaceutical company that wants to take on this approach," Swerdloff said. "The reasons for that, in my opinion, are the same reasons that in general there have been very, very few new contraceptions for men, or even for women."
Swerdloff believes that -- unlike a new cancer drug that people need and would pay big money for -- pharmaceutical companies don't see the profits in male contraception investments when healthy people already have relatively cheap, safe options for women's birth control or other methods.
"There would be a considerable up-front cost," Swerdloff said.
But at least all doctors can agree that one thing male contraception research isn't missing is interest by the public.
"We don't have a lot of trouble recruiting men for our studies," Amory said. "There are many couples where the woman can't use the pill for a variety of reasons, or just doesn't want the pill."
Amory believes the challenges with male contraception are much greater.
"It's a lot easier to suppress the production of one egg every month than the 1,000 sperm men make once a second, everyday," he said.
"Even when they're lying on the couch, men are actually doing something."