system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does birth control make you gain weight?

Does it increase your appetite, therefore making you eat more and gain weight? Or do the hormones affect the way your body processes calories? How does that happen and why?
gpt
For starters, almost all forms of birth control DO NOT cause weight gain! It's a widely held misconception, but when compared to a control group, women on birth control gain the same amount of weight.

That being said, there *is* one form that causes weight gain: Depo Vera (the shot). In fact, about 25% of patients experience weight gain!
There's not a whole lot known as to *why* this happens or if it's a change in appetite or metabolism, but it's probably related to progesterone.