The quantities found in each tissue are dependent on the water content in the tissues. One should be moderate in his or her caffeine consumption, because with each sip of a caffeine-containing drink, the ovaries, or fetus in the womb of a pregnant woman, or testes are bathed in caffeine at varying concentrations. The use of caffeine to counteract the effects of alcohol seems to have its roots in folklore, as laboratory experiments show clearly that a dose of caffeine in rabbits and rats significantly increases the impairment of performance caused by alcohol. If the traditional sobering effect of coffee is real, it must work despite the caffeine present. And this may in fact be so, as coffee has been used for years as the sobering drink, though tea contains almost the same amount of caffeine per cup.
Caffeine does stimulate the human nervous system and causes a feeling of wakefulness.
Any substance we consume so much of warrants investigation of any harmful effects it may have on us, and such is the case with caffeine.