system
Given the following post, respond as if you're commenting on Reddit:
human
When a person develops an alcohol tolerance by drinking frequently, does that mean their BAC is actually lower after a drink than the average person?
gpt
Acquired alcohol tolerance is caused by several different mechanisms. The first and probably most important is just behavioral compensation. Frequent heavy drinkers tend to automatically adjust certian kinds of behaviors and learn techniques, ways of acting and processing information, that make them appear less drunk to others and even feel less drunk themselves.

There are also chemical mechanisms of tolerance that can change in response to regular drinking, too, though. In the central nervous system, changes to the density of certain receptors and enzyme pathways will dampen the effects of ethanol. There's a fine line between these changes and behavioral compensation. They're really probably the same thing, but at different scales.

These mechanisms don't reduce the amount of alcohol, they just change the way the person acts in the presence of alcohol. However, there are also metabolic tolerance mechanisms, like the proliferation of cells in the liver that have upregulated production of alcohol dehydrogenase. This mechanism will lead to a faster breakdown of alcohol that enters the body and so prevent BAC from getting as high even if the same amount of alcohol is consumed.

In most cases, all of these mechanisms are happening in combination, though very heavy drinkers will eventually reverse their metabolic tolerance once liver damage becomes severe enough.