I have been looking for an analysis like this forever (obviously, this assumes that you’re not worried about STDs, only pregnancy):
Given that the condoms represent only about 0.001 percent of the 152 million tons of trash American households produce annually—and that we still need a lot of research into the precise effects that pharmaceuticals are having on our water supply—condoms seem to be the greener choice. This is especially true when you factor in all the packaging that typically comes with American pharmaceuticals—the plastic dispensers, the printed instruction leaflets, and so on.
Luckily, there is one clear champ in this contest. Among the nonpermanent forms of contraception, the one that is least wasteful and most effective—that is to say, the greenest—is the copper intrauterine device. The copper IUD is hormone-free; made from a small amount of a cheap, plentiful metal; and can last up to 10 years. It’s also 99 percent effective in typical use, as compared with 82.6 percent for condoms and 91.3 percent for the pill. Nevertheless, less than 2 percent of contraception-using women in the United States use copper IUDs.
This would also seem to allow you to avoid the awkward effect the pill can have of making you think you’re attracted to your mate, only to get off the pill and realize your non-pill-modified chemistry thinks he’s gross.
Still, I’m sure IUDs come with their own, varied problems, but this is still an angle I’ve been curious about for some time (especially re: the amount of waste created by condoms vs. impact of additional hormones in waterways).
Or, you know, you could just not have sex. But that would be horribly rational of you, dear animals.