I drink unsweetened iced tea, maybe 40mg of caffeine in a serving. I might drink one or two a day for a month or two then none for weeks. never noticed any withdrawal type of symptoms, maybe not enough caffeine or enough time drinking it. I'll use caffeine tablets 100mg as a stimulant at 1/2 and full marathons, usually a tablet and a half about 30 minutes before the start and on the full taking a gel with caffeine ( 100mg ) at about 14 miles and again at 20-21 range. Seems to give a mental boost for the last 4-5 miles and help with the pain, stomach usually takes it ok, but better find a porta-john shortly after the run.
My cardiologist is not big on lots of caffeine on a daily basis, sorta ok with moderate amounts at random times.
I think it also depends how you get the caffeine, better in coffee or tea than say MT Dew with tons of sugar and an extra 300 calories.
Of course two Tylenol and a bottle of Mt Dew will make you fell pretty good for a few hours for a hockey game....followed by pizza and cold beer.