There are two types of tolerance at work with alcohol. Because of the higher metabolic rate for alcohol lower peak blood alcohol concentrations are achieved by chronic alcohol users than the average drinker when the same amount of alcohol is ingested. The second is functional tolerance in which there is an actual change in the organ or system's sensitivity to the drug. Studies have shown that chronic alcohol users can have twice the tolerance for alcohol as an average person. It is important to note however that even in light of these tolerance factors, it has been shown conclusively that even in heavy alcohol users functional impairment is clearly measurable at the blood alcohol concentration levels that are currently used for traffic law enforcement and safety sensitive job performance.
Tolerance is always a sign of growing dependence on alcohol.
Gender differences . Another gender based difference is in the elimination of alcohol.