system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why isn't a birth control pill for men invented yet?

It seems like with medical advances, someone, somewhere is either working on it, or has it in use.
gpt
Healthy women do not have an egg ready for fertilization 3/4 of the time. So a birth control pill for women just has to make this not-ready state last longer.

Healthy men always have sperm ready to ejaculate. So a birth control pill for men is much harder; it has to make your body behave in a way that it never naturally does.