Many people take caffeine always, or never. But the evidence is clear: for some tasks, drink coffee -- for others, don't.
Caffeine:
- Impairs hippocampal neurogenesis and long term memory
- Narrows focus -- aiding short-term memory when the information is related to the current focus of thought, and making short-term recall more difficult when the information isn't related
- Increases short term recall of both true and false memories
- Increases short term memory and attentional control
- Increases memory retention and retrieval
So:
Use caffeine for short-term performance on a focused task (such as an exam).
Avoid caffeine for tasks that require broad creativity and long-term learning.
(Disclaimer: The greater altertness, larger short-term memory capacity, and eased recall might make the memories you do make of higher quality.)
At least, this is my take. But the issue is convoluted enough that I'm unsure. What do you think?
There are conflicting issues though. There are studies (that I read years ago, and have no link to) that show that consistency is better... that consistent low-level caffeine drinkers are more alert than their non-caffeine colleagues, but less jittery than high-caffeine people (optimum seemed to be 2-3 cups per day).
Associated with that would be method of consumption: concentrated does (espresso) v. sipping american coffee over an afternoon. Using is in a "targeted" manner might fail you: If you are not particularly used to the effects and suddenly drink coffee for short term memory reasons, you might not get the desired result because you'd be too "hepped-up" (to use the technical term...ha!).
If you ARE used to drinking coffee, and suddenly avoid it for long term learning reasons, you might be either sleepy or hit withdrawal.
The sensitivity to irregular caffeine users is just due to lack of tolerance. It can still be avoided by just reducing the dosage compared to regular caffeine users.