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At a meeting of endocrinologists this month, researchers presented new work that suggests they’re one step closer to a male birth control pill! Do you feel like you've heard this news before?

Well, that's probably because you have. Scientists have been looking into a safe, reversible kind of male birth control for decades and they've gotten close, but not quite there. Even here on SciShow, we’ve reported on things like chromatin remodeling, hormone injections, and a dissolvable gel that plugs up the vas deferens — AKA the sperm tubes.

Researchers call these treatments “male birth control” for short, because they’re tested in cisgender males who are making sperm. So why’s it so tricky to make a male pill? The short answer is: it's a lot easier to stop one egg a month than millions of sperm a day.

The female birth control pill has been around since 1960 — nearly 60 years ago! And it’s one of many options out there. The pill has synthetic hormones — either a combination of estrogen and progestin, or progestin alone.

So it stabilizes hormone levels and prevents the spike in estrogen that normally happens midway through the menstrual cycle, setting off a chain of events that lead to ovulation. Without that spike, no egg is released and no babies are made. Very rarely, the female birth control pill can have serious side effects, like blood clots or heart problems.

But it has some potential health benefits too, like reducing bone thinning, anemia, or risk of some cancers. Other than condoms, vasectomies, and withdrawal… there aren’t many male birth control options. And nothing based on hormones has panned out.

On average, men release around 180 million sperm every time they ejaculate. It only takes one to fertilize an egg and get their partner pregnant. So… that's a lot of sperm to deal with.

Instead of physically stopping them, like a condom does, male pills aim to lower the sperm count. Basically, stopping the production of sperm cells, but leaving the rest of the semen alone. And the basic strategy for this is kind of counterintuitive.

It turns out that if you give men lots of testosterone, they stop making sperm. Sperm are produced in the testes, which are also testosterone factories. So testosterone levels are really high in there, like 25-125 times higher than in blood.

And sperm need those high concentrations of testosterone to develop correctly. But when a dude gets an injection or a pill of extra testosterone, the brain and pituitary gland sense that body-wide levels are high enough and shut off production in the testes. With no testosterone being made down there, the concentration drops, and sperm don’t develop.

Previous attempts at male hormonal contraception involved weekly or monthly doses of synthetic testosterone. And if you add progestin, these injections, implants, or patches worked even better. But even though they were good at stopping sperm production, there were drawbacks.

It was difficult to get synchronized, steady levels of testosterone and progestin. And weekly, or even monthly, injections aren’t as convenient as a daily pill you can take at home. Birth control doesn’t work if you can’t get people to use it.

Plus, some men had unpleasant side effects like pain at the injection site, acne, or changes in mood including more aggression. Researchers were wary of giving the necessary big doses of oral testosterone, too, because previous studies have shown that this can be really hard on the liver. Not to mention, the body clears this orally-delivered testosterone pretty quickly so pills have to be taken twice a day.

So what makes this new male pill different? This research is a team effort from scientists at the University of Washington and the Los. Angeles Biomedical Research Institute.

And they presented their work at the recent Endocrine Society meeting in Chicago. Their experiments focused on a compound called dimethandrolone undecanoate or DMAU. It has a different structure than testosterone that lets it hang around in the body longer, which keeps levels steady even if it’s only taken once a day.

DMAU is considered a pro-drug, because it's converted to an active molecule that interacts with the body after it's ingested. In this case, enzymes called esterases change DMAU into dimethandrolone or DMA. And DMA binds to the same hormone receptors as testosterone and progestin throughout the body.

Just like testosterone given in a pill or injection, DMA tricks the body into producing less testosterone in the testes, so concentrations there drop and sperm aren’t produced. When the researchers tested this in animals it worked pretty well. It even stopped sperm production in rabbits, who have legendary fertility.

Sounds promising, right? This research is getting a lot of attention, but it's still in the early stages. Here’s how the recent experiment went down: researchers had 83 men between ages 18 and 50 take DMAU pills daily for 28 days.

They also took blood samples before and after, to check for hormone levels and other health markers like cholesterol. And the scientists found that the testosterone in the participants’ blood decreased to very low levels — levels that suggested that sperm production was effectively shut down. Now, it's important to note though that they didn’t actually measure sperm count.

This study was mostly to test whether the pill is safe. And it seems like it is! The participants didn't report any significant changes in sex drive, sexual function, or any serious side effects with their livers or kidneys, which were all potential concerns.

Some men had mild weight gain and increased red blood cell count. And some had slightly decreased levels of the good form of cholesterol, but these weren’t serious problems. The research team is starting another study soon that will follow men taking the DMAU pill for a longer period of time, and take semen samples to measure their sperm production.

So whether it’s this team or another than makes the breakthrough... safe, convenient, reversible male birth control will definitely be a pretty big deal. And you know who else is a big deal? SR Foxley, our SciShow President of Space.

He’s actually pretty humble, but he’s a big deal to us because he helps make SciShow possible every month so we can bring you the latest in science news and dig deep into big questions. Thanks SR! You are the best!

And to learn more about how you can help us out too, check out patreon.com/scishow. [♪ OUTRO ].