Friend of mine helps out rehabilitating kids from broken homes, once met him with a 17 year old guy who had been drinking about 25 cans of monster a day since he was 10-12. Guy barely had any teeth in his mouth, and seemed to permanently twitch.
Moderation is key with stimulants. Just like you wouldn't (shouldn't) pound down pre-workout every work-out since it just creates dependencies and lessens the actual effect, yet with increasing health effects.