I'm pretty sure that's the case, at least for myself. If I drink coffee every day, then I have normal levels of mental function when I am on caffeine and lower

I'm pretty sure that's the case, at least for myself. If I drink coffee every day, then I have normal levels of mental function when I am on caffeine and lower than normal at other times. I like coffee though and decaf just doesn't have the flavor, so I alternate weeks with and without coffee. Seems to work for me.