Cross-Price Elasticity of Sexual Demand

Via jwz comes this story of a crazily effective birth control method for men:

The procedure called RISUG in India (reversible inhibition of sperm under guidance) takes about 15 minutes with a doctor, is effective after about three days, and lasts for 10 or more years. A doctor applies some local anesthetic, makes a small pinhole in the base of the scrotum, reaches in with a pair of very thin forceps, and pulls out the small white vas deferens tube. Then, the doctor injects the polymer gel (called Vasalgel here in the US), pushes the vas deferens back inside, repeats the process for the other vas deferens, puts a Band-Aid over the small hole, and the man is on his way.

...

[T]he polymer lines the wall of the vas deferens and allows sperm to flow freely down the middle (this prevents any pressure buildup), and because of the polymer’s pattern of negative/positive polarization, the sperm are torn apart through the polyelectrolytic effect. On a molecular level, it’s what supervillains envision will happen when they stick the good guy between two huge magnets and flip the switch.

With one little injection, this non-toxic jelly will sit there for 10+ years without you having to do anything else to not have babies. Set it and forget it. Oh, and when you do decide you want those babies, it only takes one other injection of water and baking soda to flush out the gel, and within two to three months, you’ve got all your healthy sperm again.

I'd predict that if this became widespread among young single men, the rates of STDs would increase a lot.

My guess is that the risk of pregnancy motivates people to wear condoms a lot more than STDs do. At the point that the average guy is about to get laid, the prospect of 18 years of child support payments concentrates the mind in a way that the unlikely event of getting chlamydia doesn't.

Condoms are nobody's idea of the ideal contraceptive. But the reason that guys want to use them is that they don't generally want to rely on the fact that the girl is on the pill or will take the morning after pill. And for good reason too - maybe they forget to take the pill, or maybe they're just crazy (in which case you've got the worst scenario - having a kid with a nutcase). But either way, there's a tail risk of bad outcomes that's now beyond the guy's control.

But if the guy knows he doesn't face pregnancy risk for any of his sexual partners, my guess is that the rate of condom use will drop off a cliff, with a resulting spike in STDs. (I tried to find estimates of condom use for straight and gay men to get a crude approximation of what the effect of removing pregnancy risk might be for condom use, but a few minutes of googling didn't turn up an obvious answer).

The only thing that makes me guess that this won't happen is that having an injection into your scrotum seems more likely for a man in a long-term relationship (e.g. as a vasectomy substitute) than for single men (e.g. as a condom substitute).

I'm guessing that the doctors treating STDs would probably be privately relieved.