Developing a tolerance to alcohol is your body's way of adapting to alcohol use. The intoxicating effect of alcohol decreases as a result of continuous consumption. Your system adapts to alcohol very quickly, as the fact that it has accustomed itself to alcohol is evident even during a single occasion of intoxication. The tolerance is not permanent; it decreases with time as you stop using alcohol or cut down on your consumption.
Your body has several means of neutralizing the effect of alcohol. The best known of these is metabolic tolerance, where the body aims at neutralizing the effects of alcohol by accelerating the rate with which it metabolizes alcohol. Metabolic tolerance slowly develops as a result of prolonged, high-scale consumption of alcohol.
The most important means is the neural tolerance where the tolerance of the brain and the rest of the nervous system increases. The nervous system tries to function normally in spite of the alcohol. This is why it will before long adapt itself to the alcohol in the body. The intoxicating effect of alcohol decreases. Prolonged, high-scale consumption of alcohol is not needed in order for neural tolerance to develop: occasional, repeated drinking is enough.
The environment where alcohol is consumed may also be important for the development of tolerance. When you drink alcohol in a certain environment, you subconsciously make a connection between intoxication and that particular environment. This is why the nervous system knows how to neutralize the effects of alcohol only in those circumstances.
National Institute for Health and Welfare