Various food consumption surveys show caffeine consumption patterns have not changed significantly over the last decade. Caffeine consumption averages around 200 mg. per day, and pregnant women tend to consume less caffeine than the general population. Depending on the amount consumed, caffeine can be a mild, central nervous system stimulant. Since caffeine does not accumulate in the body over the course of time, it is normally excreted within several hours of consumption. Any pharmacological effects of caffeine are brief, usually passing within hours.
People differ greatly in their sensitivity to caffeine.
With regular use, tolerance develops to many of the effects of caffeine. For example, a person who consumes caffeine on a regular basis may drink several cups of coffee in a few hours and notice little effect, whereas a person who isn't a regular coffee drinker may feel some stimulant effect after just one serving. When regular caffeine consumption is abruptly stopped, some people may experience symptoms, such as headaches, fatigue or drowsiness. These effects usually are temporary, lasting for a few days, and often can be avoided if caffeine cessation is gradual. Overall, individuals tend to find their own acceptable level of caffeine.