• Male birth control pills have been researched for some time, however previous attempts have been found to be ineffective.
• A new method that concentrates at blocking male sperm ejaculation, has been found to be effective in mice. A drug could be administered orally, just like the female version.
• Before a male birth control pill can be released for humans, it will take a lot of time.

Armada of sperm headed for the egg. A birth control pill for men would stop ejaculation. Photo credit: blog.f1000.com

When ‘the pill’  appeared in the early 1960’s it  stirred a sexual revolution, while also offering a fantastic family planning tool. To this day, it is the most reliable contraception method and safe to use (almost), however as you might imagine it was a rather bumpy road at the beginning. Obviously, birth control pills are exclusively available to women, but why not a pill for men too? The challenges are numerous, and previous attempts showed numerous flaws and side effects. A new research by scientists at the Monash University in Australia took an alternate route at developing a possibly viable birth control pill for men by blocking sperm ejaculation, instead of sperm production. Findings show promising results in tests on mice, however we might be many years away from seeing such a product on the market.

The pill

Birth control pills work through several mechanisms, with their primary purpose being to stop ovulation. Since no egg is released, sperm fertilization is impossible and thus the woman can’t get pregnant. To do this, most pills release synthetic forms of estrogen and progestin. These exclusively female hormones stabilize a woman’s natural hormone levels indifferent of menstrual cycle. For the egg to be released by the ovaries, other hormones need to be signaled by an estrogen bump which typically occurs during mic-cycle. So simply by normalizing estrogen levels and avoiding a peak, the egg isn’t released and pregnancy is totally avoided.

Things a lot more complicated with men, and not just because estrogen doesn’t work on men – not in the way you’d want at least. For one, we’re not talking about stopping an egg from being released once a month. A birth control pill for men would need to stop each of the 1,500 sperm cells men produce each second. Hormonal treatments similar to the mechanics of the female version have proved to be clumsy, and produce numerous side effects. Attempts at halting the rapid production of sperm is similarly difficult, in part because a natural barrier between the blood and the testis, the site of sperm production, keeps drugs out.

Blocking ejaculation

A team of researchers led by  Sabatino Ventura of Monash University in Australia took an alternate route. Instead of concentrating on stopping sperm production, the scientists decided to look for a way to halt sperm ejaculation altogether. Sperm is produced inside the testicles and then stured in a coiled tube called the epididymis. During ejaculation, smooth muscles contract and propel the sperm out the epididymis, through a tube called the vas deferens, then into the urethra from which it is finally expelled. Muscle contraction is signaled by certain hormones which attach themselves to two receptors: α1A-adrenoceptors and P2X1-purinoceptors.

Previous attempts tried to block only the α1A-adrenoceptors, but tests on mice showed that  sperm still made its way to the urethra. Scientists suggest that the other receptor is compensating, leading to fertilization 50% of the time. For their study, Ventura and colleagues bred mice which were genetically modified to block both receptors. Both female and male mice were born lacking the two receptors and proceeded to mate as usual. It was found that female mice could still become pregnant following artificial insemination.

The modified males, however, didn’t fertilize the females. Closer inspection showed that the males’ vas deferens did not contract normally in response to stimulation, suggesting that the lack of receptors did stop sperm movement. What about side effects? Well, the two receptors are known to be linked to cardiovascular health, but males’ blood pressure only dropped by 10%.

Because the vas deferens is located  outside the blood-testicle barrier, this also means drugs that target these receptors could be administered orally – essentially,  a male birth control pill would thus be possible. More work will be required to test the side effects more thoroughly before clinical trials on human may begin – which will take many years no doubt.  In fact, drugs that block α1A-adrenoceptors are already on the market to treat benign prostate enlargement.

Even if a birth control pill for men would be release tomorrow with no side effects and completely reversible, there is still a big challenge in the way of its wide-scale usage. Of course, there is a psychological factor involved – men are very proud of their reproductive capabilities and being unable to ejaculate might not be the most appealing prospect for most.

“A lack of ejaculate has the potential to be disconcerting,” the researchers wrote in their study.

The findings were reported in a paper published in the journal Proceedings of the National Academy of Sciences.