I can't have caffeine after 1 PM without it messing with my sleep schedule. That's been true for a long time. I used to seriously overdo the caffeine and that probably contributed to having much bigger mood swing problems in the past.

I've reduced my overall caffeine consumption to a 1.5-shot espresso in the morning, and with proper meds I can keep it there. Well, I do drink white/green tea sometimes, but they are fairly low caffeine compared to coffee or black tea.

The proper meds part is related to ADD treatment. Caffeine is a substitute stimulant that helps with focus, but for me it interferes more with sleep than amphetamines do, and makes me more jittery as well. I recently noticed I was consuming more and more caffeine later in the day - I told the PA about it as part of the justification for asking for an adjustment to the stimulant meds.