Most people think of contraception as an issue of women’s health and rights. But for millennia, men too have wanted choices — the means to decide whether, when and with whom they father a child.
Coitus interruptus or the withdrawal method, was practiced as early as 2,500 years ago, and from the 18th century till modern times has been one of the most common forms of contraception. Condoms, made first of linen or intestine, date to at least the 16th century. But today coitus interruptus, condoms, vasectomy and abstinence are still the only methods of contraception available to men. As Sightline Institute in Seattle put it, “Male contraceptive options haven’t changed since Elvis was thin, cars had fins, and Ike was stumping for your vote.”
Today almost a third of American couples rely on the man to prevent ill-timed or unwanted pregnancy, but for young men who may want a child in the future, the options stink. Condoms are the best means available to prevent STIs, but in any given year one in six couples relying on condoms will end up with an unplanned pregnancy. Withdrawal and episodic abstinence (the rhythm method) fail even more often because they are so hard to do perfectly. Vasectomy is highly effective, but since reversal may not work, it’s not an option for men who don’t already have the family they want.
By contrast, “get it and forget it” methods for women drop pregnancy risk below 1 in 500, have bonus health benefits, and return normal fertility. When it comes to people being able to manage their fertility, we are a long way from gender equality.
The good news is that the last decade has brought increased understanding of male reproductive physiology and revealed potential new methods to safeguard against an ill-timed pregnancy. No single method will ever fit for everyone, but a variety of potential contraceptives (mechanical or pharmaceutical, shorter or longer acting, reversible or permanent, some enhancing libido or sexual function and some sexually neutral) could offer men real choices that fit their age, culture and lifestyle. Some may even have bonus health benefits like increasing energy and muscle mass or preventing balding.
In addition, modern information technologies invite novel educational approaches and distribution channels for medical services including contraceptives. Technology now allows personalized education through the Internet and deliveries in hard-to-reach geographic locations, such as drone shipments to remote locations around the world. Social media opens up new opportunities to generate dialogue about men and contraceptive choice and the broader issue of intentional parenthood.
We finally may be at the point that a serious investment in male contraception could create real options for the half of the world’s population that currently has to rely on condoms, vasectomy, withdrawal, abstinence, or a trusted partner. Imagine if all people, regardless of gender, could enjoy sexual intimacy and pleasure without the worry of an unexpected pregnancy? Imagine if each person, regardless of gender, could fully choose if or when to become a parent, and with whom?
How might that work?
Potential Targets and Methods of Male Contraception
Male reproductive physiology offers three broad targets for contraception. A potential contraceptive can target the production of sperm itself, or the maturation and function of sperm, or the transport of fully developed sperm out of the male body. Within each of these three broad targets lies a range of more specific targets and mechanisms for preventing unwanted fertility. Some potential contraceptive approaches are hormones, some are drugs and some are mechanical. Each is in very different stages of research and development.
Contraceptive approaches seeking to switch off sperm production:
- Testosterone
- Synthetic androgens such as MENT
- Testosterone-progestin combinations
- Antagonists of gonadotropin-releasing hormone (such as Acyline)
Approaches that affect maturation and function of sperm:
- BET protein inhibitor JQ1
- Retinoic acid synthesis inhibitors
- Lonidamine derivatives–Adjudin and Gamendazole
Approaches that target a sperm’s ability to travel towards the egg:
- CatSpers
- Polymer barriers
- Mechanical barriers
- Clean Sheets Pill
- Epididymal Protease Inhibitor (EPPIN)
Turning off sperm production with a hormonal switch
Sperm production begins in puberty and continues through adulthood, maintained by high levels of testosterone within the testes. The entire process takes between 74 and 120 days, and the testes produce 200 to 300 million sperm each day. That’s about 1,000 sperm for every heartbeat! (Think of this in contrast with the monthly ovulation cycle of women and the relative ease of targeting a single egg issued by a woman each month by comparison.)
Complex hormonal interactions between the hypothalamus, the pituitary, and the Leydig cells in the testes bring this about. These interactions are summarized in the figure that follows.
Figure 1 Hormonal Regulation of Spermatogenesis
Source: Opentextbc.ca
Testosterone: Given that testosterone is so key to male reproduction, an obvious first choice of a reversible male contraceptive is testosterone itself. Most hormonal methods of male contraception seek to create a negative feedback loop that by increasing testosterone elsewhere decreases testosterone in the testes. The aim is to lower testosterone inside the testes while maintaining normal levels in the body as a whole. Possible modes of administration include injections, biodegradable microspheres, and implants which, when placed just below the skin, would work for 4-6 months. Testosterone is effective and reversible, but to date minimizing negative side effects has been a challenge.
Synthetic androgens: Androgens are the general class of hormones to which testosterone belongs. Some synthetic androgens suppress spermatogenesis at lower doses and with fewer side effects than testosterone. And some work better in combination with another class of hormone, progestins. The ideal androgen and the ideal mode of administration are still being investigated. MENT is a promising synthetic androgen that is being developed as a subdermal implant.
Gonadotropin-releasing hormone-based contraceptive therapy: Gonadotropin-releasing hormone (GnRH) is a pivotal hormonal control that turns on fertility by increasing levels of other hormones including testosterone in the reproductive system. Acyline and related drugs are GnRH antagonists, meaning they inhibit the action of GnRH. This class of drugs has potential for fighting prostate cancer and turning off unwanted sperm production.
Altering Sperm Maturation and Function
To understand the next class of targets, those that alter sperm maturation and function, it is helpful to know a bit more about where and how sperm development takes place.
