Long-term drinking can leave permanent damage, causing the brain to shrink and leading to deficiencies in the fibers that carry information between brain cells. Many alcoholics develop a condition called Wernicke-Korsakoff syndrome, which is caused by a deficiency of thiamine (a B vitamin). This deficiency occurs because alcohol interferes with the way the body absorbs B vitamins. People with Wernicke-Korsakoff syndrome experience mental confusion and lack of coordination, and they may also have memory and learning problems.
The body responds to the continual introduction of alcohol by coming to rely on it. This dependence causes long-term, debilitating changes in brain chemistry. The brain accommodates for the regular presence of alcohol by altering neurotransmitter production. But when the person stops or dramatically reduces his or her drinking, within 24 to 72 hours the brain goes into what is known as withdrawal as it tries to readjust its chemistry. Symptoms of withdrawal include disorientation, hallucinations, delirium tremens (DTs), nausea, sweating and seizures.
To learn more about how alcohol affects the brain, see How Alcohol Works.