Ever wonder why there’s no birth control pill for men? For starters, it’s a math problem: To stop a woman from getting pregnant, all you have to do is block a single egg each month. But a man produces millions of sperm each day -- about 1,000 every time his heart beats. Blocking them all is a much bigger task.

This helps explain why no one has come up with a reversible form of birth control for men since the condom was introduced centuries ago. (The first unambiguous description of the prophylactic’s use appears in a 1564 writing called “De Morbo Gallico,” which describes a syphilis outbreak in Europe that began in France in the 1490s.)

But a new option may now be on the horizon. A study published in Friday’s edition of the journal Cell describes an experimental drug that, when taken daily by male mice, reduced their sperm count so much that the animals were rendered effectively infertile. When the drug was stopped, sperm counts and quality were restored and the mice were able to sire healthy offspring.

The drug is a small molecule that the researchers have dubbed JQ1. Due to its small size, it is able to cross the blood-testis barrier and reach the cells where sperm are produced. Once in place, JQ1 appears to bind with a protein called BRDT, disrupting its normal function and ultimately preventing sperm cells from maturing.


A 2007 study found that messing with the BRDT protein in mice caused the animals to become sterile. Another study from 2010 showed that JQ1 and other small molecules could target proteins like BRDT. So an international team of researchers led by Dr. Martin Matzuk of Baylor College of Medicine in Houston put it all together and confirmed that JQ1 reduced sperm production.

When seven male mice were given a daily dose of 50 milligrams of JQ1 per kilogram of body weight, only four of them were able to sire offspring, and the litters were smaller than usual. When the daily dose was doubled, none of these four mice were able to reproduce at all.

By comparison, seven control mice which were not on the drug sired more than twice as many litters of pups, and the litters were normal-sized.

All of this was accomplished without affecting the animals’ hormone levels or sex drive -- essential conditions for any birth control pill that human males would be willing to take (and that drug companies would be willing to develop).


Within three months of stopping treatment, all seven of the experimental mice were able to sire offspring. The babies whose fathers were treated with JQ1 had “normal size, activity, and behavior as offspring born from controls,” according to the Cell report.

Of course, mice are not people, and it’s not yet certain that this approach will work in humans. But Matzuk and his colleagues are optimistic that it will because the BRDT proteins in mice and men are very similar. “We envision that our discoveries can be completely translated to men, providing a novel and efficacious strategy for a male contraceptive,” they concluded.

In a commentary that accompanies the study, Dr. William Bremner of the University of Washington in Seattle shares their optimism. He called JQ1 “an exciting new approach to male contraception.”

If these experts are right, there is reason to believe many men would embrace a birth control pill. About one-third of couples currently rely on some form of male-centric birth control -- either condoms or vasectomy -- demonstrating that men are willing to take an active role in preventing pregnancy.


Return to the Science Now blog.

Follow me on Twitter @LATkarenkaplan