No matter how committed you are to gender equality, women's experiences of sex differ from men's in a major way: They typically involve birth control.

This can feel very unfair. Why isn't there a pill for men? Isn't it their turn?

As it turns out, the comparative lack of male contraceptive options isn't just the result of gender inequality.

Writer Susan Rinkunas neatly explained on New York magazine's The Cut why creating reversible male birth contraception has proved challenging:

"Women usually release one egg per month, but men can produce 1,000 sperm per second. The target is a lot bigger."

It only takes small doses of hormones to flip the "on-off switch" in women that stops the ovaries from producing eggs, according to a recent episode of the Marketplace and Quartz podcast "Actuality." These hormones work by essentially tricking the body into thinking a woman is pregnant.

Men's testes, on the other hand, do not ever naturally stop producing sperm. It takes much larger doses of hormones to shut them down, which come with more severe side effects, Rinkunas reported.

For this reason, recent scientific efforts to develop reversible male contraceptives have focused on non-hormonal methods.

There are three promising approaches, David Sokal — chair and director of the Male Contraception Initiative — told Actuality. They are:

1. Vasalgel, an injection that blocks the emission of sperm.
2. Eppin, an inhibitor that prevents sperm from swimming.
3. Cyclosporine A and FK506, immunosuppressant drugs that cause sperm to mature with deformities that prevent pregnancy.

So why haven't any of them hit the market?

Male contraception has yet to leave the realm of academic research because of technical and financial issues.

Big Pharma lost interest in developing male contraceptives between 2005 and 2008, Emily Dorman of the Male Contraception Initiative told Actuality. Without major pharmaceutical companies footing the bill, those working in the field often have to seek backing from private investors, The Atlantic reported.

"Funding is the key issue," Sokal told ATTN: via email:

"Currently, with Big Pharma out of the picture, the only major funding is coming from [the National Institutes of Health]. Aside from NIH, [The Bill & Melinda Gates Foundation] has provided about $40 million to FHI 360 for developing new female contraceptives, but nothing significant yet for men."

"Incidentally, the Michelson Found Animals Foundation is putting about $70 to $100 million into research for dogs and cats," Sokal added. "Researchers such as Kevin Eisenfrats at Contraline.com and Mike O'Rand at EppinPharma.com are working to get venture funding in order to supplement NIH and other funding sources."

Some of the difficulties that face these researchers also have to do with the fundamental nature of studying contraception, Dorman said.

It can even take healthy couples who are trying to get pregnant a long time to conceive. So when you design a reliable study about contraception, you're looking at years of clinical trials before something hits the market.

Nonetheless, surveys on male contraception report that a significant number of men are interested in using it, and almost all women would trust their partners to take it responsibly.