After chronic alcohol consumption, the drinker often develops tolerance to at least some of alcohol's effects. Tolerance means that after continued drinking, consumption of a constant amount of alcohol produces a lesser effect, or increasing amounts of alcohol are necessary to produce the same effect. Humans and animals develop tolerance when their brain functions adapt to compensate for the disruption caused by alcohol in both their behavior and their bodily functions. This adaptation is called functional tolerance. Chronic heavy drinkers show functional tolerance when they have few obvious signs of intoxication even at high blood alcohol concentrations, which in others would be incapacitating or even fatal. Functional tolerance, however, does not develop at the same rate for all alcohol effects. Consequently, a person may be able to perform some tasks after consuming alcohol while being impaired in performing others. Although tolerance to most alcohol effects develops over time and over several drinking sessions, it also has been observed within a single drinking session; this is called acute tolerance. The development of tolerance to alcohol's effects over several drinking sessions is accelerated if alcohol is always administered in the same environment or is accompanied by the same cues. The development of tolerance also can be accelerated by practicing a task while under the influence of alcohol. Exposure to large quantities of alcohol can lead to the development of functional tolerance independent of environmental influences. Tolerance that results from a more rapid elimination of alcohol from the body is called metabolic tolerance. Studies suggest that the potential to develop tolerance to alcohol is genetically determined and may contribute to increased alcohol consumption. 30 references