Say what you will about size, it's the numbers that really matter. Consider:
Women produce one egg a month, which birth control pills have been notably efficient in keeping corralled.
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Men, however, come armed with hundreds of millions of sperm, so a successful male contraceptive has to deal with every one of the little buggers. Every one of them!
Little wonder, then, that promises of a male pill have rung as hollow as a morning-after's "I'll call you."
The sexual landscape may be changing, though, thanks to a University of Minnesota chemist who has developed a new approach to bringing men into the world of birth control, short of condoms or vasectomies.
Gunda Georg is a professor in the College of Pharmacy's Department of Medicinal Chemistry. She's also the one behind the joke that every room of the six-story building is used for research, "even the bathrooms." (More on that later.) The National Institutes of Health recently awarded Georg a $4.7 million grant for her contraceptive work.
In a nutshell, here's what's new: Most efforts to develop a male contraceptive use testosterone, but there are side effects: moodiness, which causes researchers to worry, or testicular shrinkage, which causes marketers to despair.
Also, men make sperm until the day they die, so any method may be used far longer than women's birth control. Finally, any method's effect has to be reversible.
Working with Joseph Tash at the University of Kansas, Georg found a nonhormonal compound called H2-gamendazole that causes developing sperm to be released before they're fully mature. "We're not targeting their generation, but their motility," Georg said.
The beauty of slowing the sperm involves another number: During unprotected sex, semen ends up only a few inches from the back of the vagina. Yet the actual distance that the sperm must swim to reach the egg is equivalent to a man running three miles, according to "The Male Biological Clock," a book by men's health researcher Harry Fisch.
Georg's approach is to keep a wannabe Michael Phelps from ever emerging from the kiddie pool.
Would a guy really use a pill -- or injection or patch or cream -- if given the opportunity?
Elaine Tyler May is a professor of American Studies and History at the University of Minnesota and author of "America and the Pill," published in 2010. Her research supports other surveys that say men would take birth control.
"Surveys show that men would certainly be willing to share responsibility for contraception, and the risks and the side effects if they were tolerable. But up to this point, there hasn't really been a pill that has shown itself to be tolerable and reasonable," May said.