How Alcohol Causes the Brain to Shrink

Cold beer
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Multiple research studies have found that the brains of people with severe alcohol abuse disorders are smaller and lighter than brains of people who are not alcoholics. The brains of alcoholics have "shrunken" compared to nonalcoholic brains.

This brain shrinkage affects the "wiring" of the brain that is used by regions of the brain to communicate with other regions and affects the parts of the brain that allow neurons to communicate with neighboring neurons.

Some Damage Is Reversible

Although it is true that chronic alcohol abuse does cause significant brain damage, much of that damage can be reversed with abstinence and alcoholics can obtain long-term sobriety in spite of deficits in decision-making.

Hard Wiring of the Brain Shrinks

The gray matter of the brain in the cerebral cortex controls most of the brain's complex mental functions. The cortex is filled with neurons that connect by fibers to different regions of the brain and to other neurons inside the brain and spinal cord. The nerve fibers are the white matter of the brain or the "hard-wiring."

These nerve fibers have shorter, more numerous fibers called dendrites that branch out like the roots of a tree to allow the neurons to "talk" with other neurons. A neuron can communicate with as few as five or as many as 10,000 other neurons at a time.

These two parts of the brain—the white matter or hard wiring and the dendrites—are the ones most affected by the shrinkage that alcoholism can cause.

Of course, brain shrinkage is not the only damage alcohol abuse can do to the brain. Alcohol can cause chemical changes in the brain that affect the function of the neurotransmitters.

Alcohol Causes Complex Problems in the Brain

Numerous research studies, with animals and human subjects, show that chronic alcohol abuse produces several toxic, metabolic and nutritional factors that interact to cause mental deficits in alcoholics.

Some of these complex factors are still not understood completely:

  • Acetaldehyde, a metabolite of alcohol, could cause toxic effects.
  • Malnutrition, especially thiamine deficiency, could play a role.
  • Cirrhosis of the liver can also cause brain damage.
  • Head injury and sleep apnea can contribute to brain damage.

Head injuries and sleep apnea are more common in alcoholics and can add to brain damage.

Alcohol, thiamine deficiency, and cirrhosis are linked and some researchers believe they contribute in a complex manner to brain damage.

Damage Can Be Permanent and Transient

Much of the damage done to the brain by alcohol can be reversed once the person stops drinking and maintains a period of abstinence, but some of it is permanent and cannot be undone.

The most significant permanent damage caused by alcohol is nerve cell loss. Some nerve cells cannot be replaced once they are lost, and that includes those in the frontal cortex, cerebellum, and other regions deep inside the brain, according to research.

However, much of the damage alcohol causes by shrinkage can be reversed with abstinence. That includes shrinkage of dendrites, which studies have shown will begin to grow again and spread after weeks or months of abstinence. This has been linked to improved brain function.

When cirrhosis of the liver is treated, research shows that some of the brain damage it can cause will begin to reverse. Brain damage in alcoholics due to thiamine deficiency can easily be treated with doses of thiamine, but repeated deficiencies can cause some permanent damage.

Alcohol Damages Decision-Making Process

One reason that alcoholics are so prone to relapse is the damage that alcohol causes to the brain's reward system and decision-making abilities.

Research shows that chronic alcoholism chemically changes the brain's reward system to the point that the drinker's pursuit of rewards become pathological.

The result of these alterations to the brain's reward systems is that the drinker is more affected by immediate rewards instead of delayed rewards. Addictive substances such as alcohol provide immediate intoxicating rewards.

Long-term heavy alcohol consumption affects the frontal lobe functions of the brain which include inhibition, decision-making, problem-solving, and judgment. This kind of brain damage makes it difficult for alcoholics to maintain long-term sobriety.

However, research has found that alcoholics can and do overcome these impairments, as the damage to their brains begins to reverse, and they can achieve long-term, multi-year sobriety when they are motivated to do so.

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5 Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  5. National Institute on Alcohol Abuse and Alcoholism. Alcohol's Damaging Effects on the Brain. Updated October 2004.

Additional Reading
  • Bartsch, AJ, et al. "Manifestations of early brain recovery associated with abstinence from alcoholism." Brain December 2006.
  • Harper, C, et al. "The Pathophysiology of 'Brain Shrinkage' in Alcoholics—Structural and Molecular Changes and Clinical Implications." Alcoholism: Clinical & Experimental Research May 2006.
  • Siggins, GR, et al. "Ethanol Augments GABAergic Transmission in the Central Amygdala via CRF1 Receptors." Science March 5, 2004.