Colin MacKenzie M.D.
November 1, 2020

Ethanol, more commonly called “alcohol”, is a colorless and psychoactive organic compound that is the intoxicating ingredient in all liquors. Besides being used in beverages, ethanol is also used as a solvent, an antiseptic, and even as fuel.  But calling ethanol “alcohol” is actually misleading because there are many different types of alcohols, including methanol and isopropyl alcohol (or rubbing alcohol).  The suffix “–ol” is used in any organic compound that includes at least one hydroxyl group (-oh) attached to a saturated carbon atom. 

Of the three alcohols already mentioned, ethanol is the least toxic, whereas isopropyl alcohol and methanol are highly toxic with as little as 2-3 teaspoons of methanol being potentially fatal.  In this article, the term “alcohol” will refer to only ethanol. 

How is it Produced?

Alcohol is a by-product of fermentation. Fermentation is a chemical reaction carried out by yeast which are single-celled microorganisms related to the fungus kingdom.  When yeast cells consume sugar, they produce carbon dioxide gas and ethanol.  The strain of yeast and type of sugars used determine the type of alcoholic beverage produced (i.e., wine from grapes, beer from cereal grains). 

Why Do Our Bodies and Brains React with Alcohol?

What most people don't realize is that we are naturally exposed to alcohol from day one!  Our bodies produce about 3 to 4 grams of alcohol per day.  This is equivalent to about ¼ of a standard alcoholic beverage.  Alcohol is produced in our gastrointestinal tract through the action of bacteria and fungi (yeasts) as a by-product of carbohydrate metabolism.  Some researchers believe alcohol can also be produced by cells outside the GI tract.  However, the body identifies alcohol as a toxin that needs to be rapidly broken down into harmless components.  Thus, the liver, the first organ to encounter alcohol after it leaves the GI tract, has evolved various enzymes to convert alcohol to carbon dioxide and water.  Some people have an illness called “auto-brewery syndrome” where the GI tract contains excessive amounts of yeast that create intoxicating levels of alcohol in the blood stream.  

How One Drink Can Affect Your Body

One drink of alcohol will create a blood alcohol concentration of about 0.016 g/dl in the average adult.  It takes one hour for the body to metabolize this amount of alcohol. The average person will exceed the Blood Alcohol Concentration (BAC), the legal limit of 0.08 g/dl after consuming 5 drinks within one hour, and it will take about 5 hours for the body to metabolize this amount of alcohol.  The amount of physical and mental impairment for any given BAC is different for each person. Thus, some people may be impaired to drive an automobile with a BAC of less than 0.08 mg/dl.

Alcohol Statistics

Most people first experience intoxication with alcohol in their mid-teens with alcohol use disorders peaking in the mid-20s.  In any given year, the percentage of adolescents having an alcohol use disorder is estimated at 4.6% with 8.5% of adults having the disorder.  High levels of impulsivity and behavioral problems are associated with an earlier onset of alcohol use disorder and a more severe course. 

The rate of alcohol use disorder is three to four times higher in close relatives of individuals with this disorder including the children of parents who have the disorder.  Increasing rates of risk exist in those who have a larger number of relatives with the disorder, have a closer genetic tie to those relatives, and if those relatives have a more severe form of the disorder.  Low sensitivity to the effects of alcohol is also associated with higher risk. 

What Alcohol Does to the Brain and Body 

Alcohol, at high enough concentrations, is toxic to nearly every organ system. 

Gastrointestinal System 

cirrhotic liver showing fibrotic nodules

Alcohol can cause pathology of the esophagus, stomach, and intestines.  Alcohol leads to an increase in acid production in the stomach which can predispose the drinker to peptic ulcer disease.  Alcohol can also impair the integrity of the intestinal mucosa, which is the protective inner lining, and make it excessively permeable allowing molecules to enter the blood stream that otherwise should not.  In addition, alcohol can disrupt the composition of intestinal bacteria leading to the production of inflammation.  These inflammatory cells and by-products can then traverse the intestinal mucosa and travel to the liver, triggering inflammation in that organ.

In prolonged cases of exposure, inflammation can lead to scarring in the liver and pancreas.  In severe cases, over time, this can lead to bleeding inside the gastrointestinal tract leading to hematemesis (vomiting of blood) or melena (blood in the stool).  Sometimes the bleeding is so severe that it can cause exsanguination and death.  Alcohol also increases the risk of various types of cancers of the gastrointestinal system.

Cardiovascular System 

Heart & Lungs ©TelePsychiatry Associates, LLC

Cardiovascular disease is also common in alcohol use disorder.  Excessive, chronic alcohol use is associated with high blood pressure, strokes, peripheral vascular disease, high cholesterol, cardiac arrhythmias, and damage to heart muscle producing a condition called alcohol-induced cardiomyopathy which can progress to congestive heart failure.  

It is still debated whether low doses of daily alcohol use can provide protective functions for the cardiovascular system.  Some researchers suggest that early studies demonstrating cardiovascular benefits were flawed, while other studies propose that certain chemicals in red wine may function as protective antioxidants.  Either way, the medical community does not recommend that anyone begin drinking for the intended result of gaining some cardiovascular benefit. In addition, what may be good for the heart, may not be good for other organs in the body.    

Nervous System (acute alcohol intoxication) 

During times of acute intoxication, alcohol impacts nearly all brain functions.  However, certain functions show greater impairment than others.  At the level of the nerve cell, alcohol’s actions are complex.  Basically, alcohol activates inhibitory receptors (increasing inhibition) and blocks the activity of excitatory receptors (increasing inhibition).  Thus, the communication between nerve cells is impaired leading to abnormal brain function.

Frontal Lobe of Brain ©TelePsychiatry Associates, LLC

The frontal lobes of the brain are responsible for planning, organization, decision-making, and self-control. Thus, under the influence of alcohol, a person may find himself or herself having difficulty controlling emotions, being impulsive, aggressive, or engaging in behaviors they otherwise would not. 

The hippocampus of the brain is critical in memory formation and when intoxicated, a person may have trouble forming new memories, learning new material, or experience “black-outs” (loss of all memories for the time of intoxication). 

Neuron cell body, dendrites, and axon with myelin sheath (black) 

A brain structure called the cerebellum is critical for coordinating body movements and reflexes. Thus, with alcohol, you are likely to have difficulty walking predisposing you to falling or getting into auto accidents. 

The part of the brain called the medulla controls many involuntary functions such as heart rate, temperature control, and breathing.  With high enough alcohol concentrations, you may experience a decreased heart rate or suppression of breathing putting your life at risk.  Those who already have a pulmonary disorder, such as obstructive sleep apnea or chronic obstructive pulmonary disease (COPD) are at particularly high risk of complications when intoxicated.

Nervous System (chronic alcohol intoxication) 

Fifty to seventy percent of those with alcohol dependency have cognitive deficits on neuropsychological testing.  Though an unequivocal alcohol-induced brain lesion has yet to be identified, imaging studies and neuro-pathological studies provide supporting evidence for neurological changes with chronic, heavy alcohol use. 

For instance, several imaging studies demonstrate enlargement of the ventricles in the majority of alcoholics.  Other studies show a decrease in frontal lobe neuronal density and a disproportionate loss in subcortical white matter. 


Even in the developed brain, Individuals with alcohol use disorder can develop degenerative changes within the white matter causing permanent, severe memory problems, psychosis, and cognitive dysfunction. 

Several neurological syndromes due to neurological changes from chronic alcohol use have been described including Wernicke Encephalopathy, Korsakoff Syndrome, and alcoholic cerebellar degeneration.   

Alcohol and Development 

Stages of human intrauterine development

Alcohol impacts the developing nervous system differently than the developed nervous system. Alcohol is particularly toxic to the brain during any developmental stage, however, the earlier the exposure, the greater the sensitivity to the effects of alcohol.  The “white matter” of the brain includes those structures that assist in the communication between neurons and is particularly sensitive to alcohol during development.

When alcohol is consumed during pregnancy, the fetal brain can experience premature cell death and developmental delays. The human brain continues to develop until the mid-20s leaving adolescents more vulnerable to the effects of alcohol than mature adults. 



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