From Introvert Dear
“Why caffeine affects introverts and extroverts differently
The reason why caffeine affects introverts and extroverts differently basically has to do with our differing levels of neocortical arousal in the brain, according to Science of Us. In other words, it comes down to how alert or responsive we are to our environment.
In general, introverts are over the optimal level of arousal — meaning, we’re more easily stimulated — and extroverts under the optimal level.
This means that consuming any kind of central nervous system stimulant, such as caffeine or even recreational stimulants, will move us further away from our optimal level of performance.”