Here's what works for me: I used to have a donut/pastry and a 16oz (or larger) coffee in the morning. I'd feel good for an hour or so, but soon would feel jittery and spaced-out. Now, I have an 8-oz cup in the morning with a decent breakfast - but no more throughout the day. I drink my coffee slow, get a little caffeine boost, and feel energized all morning. Moderation.