Scientists have been hard at work for decades trying to develop a safe, highly effective, and reversible contraceptive for men—something akin to the birth control pill that has been available to American women since 1960. Thus far, nothing they’ve tested has been remotely ready for prime time. However, a new study just published in The Journal of Clinical Endocrinology & Metabolism suggests that they may be nearing a breakthrough.

What did they do?

Researchers reported the results of a clinical trial involving 320 men, all of whom were healthy, aged 18-45, and involved in monogamous relationships with women. Once every eight weeks, these men received a contraceptive injection, which consisted of a blend of two synthetic hormones (testosterone and progestin).

These hormones were expected to suppress sperm production—and that’s exactly what they ended up doing in most male participants. Within 24 weeks, 95.9% of men who continued receiving the injections had sperm counts of less than 1 million per milliliter (for a reference point, sperm counts under 15 million are typically considered low, which means that 1 million would be really low!).

The injection’s effects were not immediate—it took up to six months in order for sperm counts to drop to this level in some cases (and in a small number of men, they never got there). While they waited for the effects to kick in (something the researchers referred to as the “suppression phase”), men and their partners were instructed to use other forms of birth control. Compared to the female birth control pill (which can start working in a week or less), the injections these men were receiving obviously took much longer to kick in.

After each man provided two sperm samples showing that his sperm levels had been effectively suppressed, he entered what the researchers called the “efficacy phase” for up to one year. During this time, men and their partners were instructed to stop using all other forms of birth control and rely only on the shots. During that year, just four pregnancies total were recorded, translating to a rate of 1.57 per 100 couples. In other words, it was pretty darn good at preventing pregnancy!

Following the efficacy phase, men stopped receiving the injections and researchers followed them for another year to see whether normal sperm production returned. Within a year, sperm levels exceeded that critical level of 15 million per milliliter in 94.8% of participants. Some rebounded more quickly than others, though. After 6 months, about half of the men had recovered normal sperm production; however, it took less than three months for some, while others still weren’t recovered after one year (and one participant still hadn’t recovered after 4 years). So, not only does this injection take longer to kick in than the female birth control pill, but it has a much longer fertility recovery period, too.

Although this injectable contraceptive was demonstrated to be both highly effective and reversible, it came with a number of side effects. In fact, the reported rate of side effects and dropout from the study was high enough that the ethics and safety board overseeing this research recommended that the study be terminated early.

Over the course of the study, 913 “adverse events” (i.e., side effects) were reported that were thought to be related to the injections. These included acne (reported by 46%), sexual disturbances (38% reported increased libido, 4% reported decreased libido), mood disorders (17% reported emotional disorders, 5% reported mood swings), muscle pain (reported by 16%), and breast growth (reported by 6%). Less common side effects included excessive sweating, testicular pain, and fatigue.

These side effects ultimately led 20 men to voluntarily withdraw from the study early.

“This tells us that men are not only interested in using hormonal contraceptives, but that most of them are willing to put up with a few side effects, too.”

Despite the high rate of side effects (most of which were rated as mild to moderate), more than 74% of the men said they were satisfied with the contraceptive and more than 82% said they would use it if it were commercially available. This tells us that men are not only interested in using hormonal contraceptives, but that most of them are willing to put up with a few side effects, too.

Why this study has been controversial

The decision to pull the plug on this clinical trial was met with a lot of criticism, much of it centered around the idea that it seemingly reflected a double standard—that men are being protected from the side effects of birth control while women aren’t.

I understand this reasoning, but it’s important to recognize that the overall rate of side effects in this particular trial was very high—and, in fact, it was higher than the rate seen in most recent studies on female birth control methods. To the ethics and safety committee overseeing this research, the risk-to-benefit ratio just wasn’t acceptable. Remember: these committees are tasked with protecting the health of participants. Any time they see a side effect rate as high as the one observed here (regardless of patient gender), it’s going to create cause for concern.

Keep in mind that medical research today is far more regulated than it was back in 1960 when the FDA approved the original birth control pill. The lack of oversight back then allowed early versions of the pill to get away with carrying a very high risk of serious side effects—side effects that women weren’t even informed about! That was a tragedy, and it’s part of the reason why getting a drug to market today is much tougher than it used to be. We now have much stricter ethical and safety standards, and that’s something we should all be glad about.

This isn’t to say it’s right that so many women who took the pill over the last half century have experienced side effects from it. It’s not right at all. Medical researchers have done a lot to reduce the rate of side effects that women experience over time, such as by offering different versions of the pill that vary in terms of hormone level (low-dose versions are available) and the kind of hormones they contain (combined vs. progestin-only); however, they can do more.

“Both men and women want—and deserve—access to contraceptives that are safe and that don’t adversely affect their health.”

Both men and women want—and deserve—access to contraceptives that are safe and that don’t adversely affect their health. Let’s be clear about one thing, though: any hormonal contraceptive for any gender is going to carry at least some side effects. That’s just the nature of tinkering with our hormones. But our goal should always be to make side effects as minimal as possible for everyone, regardless of gender.

What’s the future of male birth control?

Although this particular injection won’t be making it to market, scientists aren’t giving up. They’re going to experiment with the hormone levels to see if they can produce a new version that will, ideally, be just as effective as the one used in this clinical trial, while carrying a lower risk of side effects.

We’re probably still a decade or more away from having a male contraceptive like this that’s commercially available, but this study is a significant step in that direction and it should provide reason for optimism that we’l
l one day truly have a male version of the birth control pill.

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