"Caffeine is a white, bitter crystalline alkaloid derived from coffee or tea. It belongs to a class of compounds called xanthines, its chemical formula being 1,3,7- trimethylxanthine. Caffeine is classified together with cocaine and amphetamines as an analeptic, or central nervous system stimulant."
"When the caffeine reaches the brain, it increases the secretion of norepinephrine, a neurotransmitter that is associated with the so-called fight or flight stress response. The rise in norepinephrine levels and the increased activity of the neurons, or nerve cells, in many other areas of the brain helps to explain why the symptoms of caffeine intoxication resemble the symptoms of a panic attack."
The Gale Encyclopedia of Mental Disorders