My goal wasn't to completely quit. The goal was to keep my caffeine intake less than or equal to 400mg (the FDA's recommended max) and to cut it off at 2pm. I didn't cold-turkey cut off caffeine.

I stopped getting acute headaches after about three days; other prolonged side effects are harder to quantify.

I should also clarify, it wasn't 800mg every day (which I realize I didn't make clear), it was just one thing where I saw that at least a few days of the last week I had consumed 800mg.