system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do birth control pills prevent pregnancy?

How does it prevent pregnancy even if a couple does unprotected sex? (I’m aware it’s not 100% effective but still)
gpt
The menstrual cycle is controlled by hormones which make sure that a single egg is released and all the processes take place in the right way. What the birth control pills does is that they replace these hormones so that you get the same hormones and a similar menstrual cycle but without an egg. Essentially you are fooling the body into thinking there is already an egg on the way.