With promising studies and changes in social norms, safe hormonal contraception for men could soon be available.

A birth control pill for men - the idea has seemed like a futuristic vision. Now, with a shift in society’s attitudes and a greater understanding of the male reproductive system, it could soon be a reality.

“We are close to having a hormonal regimen that might work for male contraception,” says Diana Blithe, director of male contraceptive research at the National Institute of Child Health and Human Development in Bethesda, Md. “The trick is to find the right combination of hormones that will completely shut down sperm production.”

There’s definitely a need for a male pill - or a cream or injection - especially in developing countries with high birthrates where polls show that up to half of pregnancies are unplanned, says Dr. William J. Bremner, director of the Center for Research in Reproduction and Contraception at the University of Washington in Seattle. Men account for about a third of contraceptive use in the U.S., and about 10% among married couples worldwide. Yet male contraceptive methods have significant drawbacks. Condoms interfere with sensation and can break, resulting in pregnancies about 15% of the time, and vasectomies require surgery and are usually irreversible, rendering a man sterile.

Still, it’s been daunting devising a hormonal male contraceptive that is as safe, effective and convenient as women’s birth control pills, which have been available since the 1960s. To prevent a woman from becoming pregnant, only one egg per month must be thwarted. In contrast, “men produce a thousand sperm every time their heart beats,” Bremner says.

In the last decade, scientists have discovered hormonal methods of temporarily halting sperm production that don’t interfere with other bodily functions. Recent surveys also indicate there is more acceptance of the notion of a male pill and that men are more comfortable talking about their reproductive health.

“Male sexuality is no longer the butt of jokes or a societal taboo,” says Dr. John Amory, a scientist at the University of Washington’s Center for Research in Reproduction and Contraception. “And because of the phenomenal success of Viagra, drug companies are more willing to bankroll research.”

Scientists in Seattle and in Europe are testing a combination regimen that stops the chemical events that prompts sperm production. In a University of Washington study, 60 volunteers received injections of progestin, a synthetic form of the female sex hormone progesterone. Progestin acts on the pituitary gland in the brain and reduces the production of two hormones that signal the testes to make sperm.

However, progestin also decreases testosterone, the male sex hormone necessary for libido and secondary sexual characteristics such as muscle bulk. So volunteers rub a testosterone gel on their shoulders every day to maintain levels of this crucial hormone.

Preliminary results have been encouraging. After three or four months, sperm counts dropped to zero in the majority of test subjects, Amory says, though the final results won’t be available until late next year. The researchers hope to achieve an overall efficacy rate of about 95%, which is comparable to female contraceptive pills.

Drug companies and university researchers alike are searching for ways to deliver the hormones in pill form. The European trial, which is being conducted by Schering of Germany and the Dutch drug maker Organon, uses the same strategy to suppress sperm but a different delivery method. The study began in January and involves 350 volunteers who have a 1.6-inch implant in their arm that contains progestin; they also receive testosterone injections every three months. Researchers hope to have results next year.

Although it will be at least five years before a male hormonal contraceptive is available in the U.S., Bremner says, the Organon/Schering implant could be approved much sooner in Europe.

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Multiple approaches to male birth control

Scientists around the world are studying various types of birth control for men.

Chinese scientists are working on a hormonal method that relies most heavily on the male hormone testosterone instead of the female hormone progestin. In a clinical trial in its final stages, 1,000 men received monthly injections of highly concentrated testosterone to turn off sperm production.

An earlier test indicated the injections dropped sperm count to zero or close to it in 296 of 308 men.

Studies of non-hormonal approaches aren’t as far along. Researchers at the University of North Carolina School of Medicine in Chapel Hill, for instance, have discovered an enzyme in sperm that is necessary for sperm movement and that could be used to develop future contraceptives. Mice bred without this enzyme produce sperm that can’t swim toward egg cells to fertilize them.

British researchers at Oxford University recently found that a drug used to treat a condition called Gaucher disease makes the sperm in male mice abnormal, rendering them sterile. That too could ultimately lead to other methods.