It's called Depo-provera, for me it was just easier, because I always forgot to take the pill. I haven't experienced any side affects, but they warn you about depression and stuff. But they did that when I was on the pill, also.
Basically you get it in your arm or hip, and only need it every three months. I've been on it for almost eight months. X.x
I was also getting bad migrains while on the pill, so this is much better for me.

I don't really know what else to say about it haha. I guess look it up if you wanna know more? After about six months of being on it most women stop having periods. X.x and it's 99% affective.