Skip to Content

Alcohol and Its Effects on Behavior


All alcohol beverages contain exactly the same kind of alcohol: ethyl alcohol, or ethanol.

Like its chemical cousins, methyl (such as Sterno) and isopropyl (rubbing) alcohol, ethanol is an organic compound containing carbon, hydrogen, and oxygen.

Chemically it is a hydrocarbon with one hydrogen atom replaced by a hydroxyl (OH) group.

The human body can metabolize ethanol relatively well, but is less capable of handling other forms of alcohol which, therefore, have a much more toxic effect when consumed.

Ethanol has been known and used as a drug for thousands of years. It is produced naturally by the interaction of yeast and sugar. In fact, small amounts of ethanol are produced naturally within the human body.

Alcohol beverages are manufactured by three different but related processes. The natural sugars in fruit juices, for example, ferment when brought into contact with yeast, and ethanol is produced until the alcohol content of the beverage reaches about 12%.

At this point the yeast is killed by the alcohol and the fermentation process stops. That is why wines produced by fermentation average an alcohol content of about 12%. The process of brewing, by which beer is made, is similar to fermentation but is carried out at a higher temperature.

"Spirits," beverages with higher alcohol concentration, are manufactured by the process of distillation, in which fermented beverages are boiled. Because alcohol boils at a lower temperature than water, it can be collected as steam and separated from the rest of the beverage.

These distilled spirits are combined with other ingredients, called congeners, to yield the many varieties of "hard liquor" such as whiskey, vodka, gin, rum, and tequila.

How Alcohol Works

Absorption : When taken in through the mouth, alcohol flows through the esophagus and into the stomach and intestine, where it is absorbed directly into the bloodstream. No digestion is required; alcohol passes right through the walls of stomach and intestine into the bloodstream.

From there it circulates to every part of the body that contains water, which is just about everywhere. The more rapidly the alcohol is absorbed, the higher the level in the bloodstream and the greater its effects.

Drinking on an empty stomach results in almost immediate absorption and rapid intoxication, whereas the presence of food in the stomach slows down alcohol's passage into the bloodstream.

Much of the alcohol still gets through eventually (although some is metabolized in the stomach or eliminated in waste products), but the absorption process is slowed by food and thus intoxication is less. ["Intoxication" here means the introduction of a toxin (poison), ethanol, into the bloodstream, which may or may not be observed in obvious behavioral changes.]

Other factors also affect absorption rate. Emotional states, for example, can change the stomach wall and cause alcohol to be absorbed more rapidly. Carbon dioxide also speeds alcohol through the stomach wall, which is why carbonated alcohol beverages have a more immediate impact.

Going Up: Intoxication

Most of the effects of alcohol which people experience during intoxication are due to ethanol's direct effects on the brain.

No specific receptor for ethanol has been identified within the brain, although some of alcohol's effects are mediated through the benzodiazepine receptors, and ethanol affects the activity of neurotransmitters such as dopamine.

Some of ethanol's effects appear to be produced by its direct action on the nerve cells themselves, probably by altering the nerve cell wall and thus the neuron's capacity to transmit information.

The higher the amount of alcohol in the bloodstream (called blood alcohol concentration or BAC), the greater the effects on the brain, other body organs, and behavior. Measuring BAC, then, can give a rough estimate of the likely effects of intoxication.

A person's BAC can be measured accurately from blood, urine, saliva, or breath samples.

Although BAC levels are often reported as decimals (such as .15), pharmacologists typically use a unit of measurement stating the number of milligrams (weight) of alcohol per 100 milliliters (volume) of blood.

This unit is called milligrams percent (literally "milligrams per hundred") and is abbreviated mg%. Thus 120 mg% means 120 mg of ethanol per 100 ml of blood. The only difference between this unit and the decimal unit is that the decimal has been moved three places.

Thus 100 mg% = .10 in the decimal system often used in the public press. Remember that this is not a percentage, but a weight to volume ratio. The decimal system is, in fact, the number of grams of alcohol per 100 ml of blood.

How do BAC levels relate to behavioral effects?

This is a very complicated question, in part because of the phenomenon of tolerance which will be discussed later. It is possible, however, to estimate the behavioral effects that will occur in a typical human drinker at various BAC levels.

In examining this list below, recognize that these effects are subject to individual variation. The BAC is influenced by many factors. Most important are the amount of alcohol consumed and the length of time taken to drink it.

Four drinks consumed in half an hour will produce a much higher level of intoxication than the same number of drinks spread out over four hours.

Body weight is also important. The larger the person, the less he or she will be affected by a fixed dose of alcohol because the drug is distributed over a larger body mass, resulting in a lower concentration of ethanol in any particular part (such as 100 ml of blood).

A 200 pound person, drinking the same amount as a 100 pound person, will be less intoxicated, all else being equal.

Characteristic Effects of Different BAC Levels

Women also tend to become more intoxicated than men who drink the same amount. One obvious reason is that women tend to be smaller. Even at the same body weight, however, women tend to reach higher blood alcohol levels than men do.

It was once believed that this was due to differences in the proportion of fat cells. Research in the 1990's, however, indicates that men have higher levels of stomach enzymes that metabolize alcohol.

This means that in men, a larger proportion of the ethanol is broken down in the stomach before reaching the bloodstream. When alcohol is injected directly into the bloodstream of men and women of the same body mass, their blood alcohol levels are identical.

In addition, the degree of intoxication reached by a woman varies substantially over phases of the menstrual cycle, with highest BAC levels reached during the premenstrual phase.

Coming Down: Detoxication

We have considered how alcohol enters the bloodstream (intoxication) and how a peak BAC is reached. But how does the BAC return to normal once a person has become intoxicated? This process is known as detoxication or detoxification, the removal of a toxin from the body.

The human body possesses a specific enzyme, alcohol dehydrogenase, that is capable of metabolizing (breaking down) ethanol. We lack such efficient enzymes for methyl or isopropyl alcohol, and so these other kinds of alcohol stay in the bloodstream for a long period of time, and can cause brain damage, blindness, or death.

BAC Level Expected Behavioral Effects

  • .02-.04 Relaxation, mild euphoria, changes in social behavior (increased gregariousness, humor enhancement); legally intoxicated in some countries
  • .055 Any positive changes occur below this limit
  • .06-.08 mg% Judgment altered, likely to take risks and actions not taken when sober; driving abilities clearly impaired; fine motor control discoordination, information processing altered, mood tends to shift from positive to negative, fantasies and motivations change, some disruption of restraint ("loss of control") for other behaviors such as eating, smoking, gambling, drugs, etc.
  • .10 Legally intoxicated in all states; reaction time slowed, color perception and visual acuity decreased, memory impairment, state dependent retrieval; driving at this BAC increases risk of a fatal crash by 10 times.
  • .12 Vomiting may occur unless tolerance is established.
  • .15 Balance impaired, slurring of speech; risk of fatal crash increases 25 times in drivers at this BAC
  • .20 Major memory impairment - "blackout" normally occurs in this range (complete memory loss), especially if BAC rises rapidly; memory does not transfer from short-term to long-term storage (this can occur at a BAC as low as .08)
  • .30 Double vision may occur; most drinkers become unconscious or fall asleep at this level, and are difficult to awaken.
  • .45 Lethal dose for 50% of adults (LD-50); death occurs due to alcohol poisoning - central nervous system inhibition of heart and breathing; death can occur at lower doses in children and adolescents.

Roughly 10% of the ethanol that a person consumes can be eliminated by stomach metabolism or waste products. Smell the breath of someone who has been drinking alcohol, and you can tell that some ethanol is eliminated through respiration, escaping from the rich blood supply in the walls of the lungs.

Some is eliminated through perspiration and other body wastes. The rest must be removed from the bloodstream by the body's "oil filter," the liver.

Alcohol dehydrogenase turns ethanol into acetaldehyde, itself a very toxic substance that is a chemical cousin of formaldehyde. In moderate doses, acetaldehyde causes reddening of the face and skin, dizziness or fainting, headache, nausea, rapid heartbeat and respiration. Larger doses can be fatal.

Fortunately the body can also break down acetaldehyde via the enzyme aldehyde dehydrogenase, turning it into acetic acid which eventually becomes carbon dioxide and water. Thus the full metabolism process turns alcohol into club soda. Through normal metabolism, the average person's body is able to decrease BAC by .015-.017 per hour.

For a 160 pound male, that is roughly the equivalent of one half ounce of ethanol per hour. The following drinks contain one half ounce of ethanol, and thus are equivalent in their effects:

  • 10 ounces of beer (5% ethanol)
  • 4 ounces of table wine (12% ethanol)
  • 2.5 ounces of fortified wine (20% ethanol)
  • 1 ounce of 100 proof liquor (50% ethanol)


Drug tolerance has to do with how affected a person is by a given dose. An individual with a high tolerance shows less effect from a fixed dose than does a person with a low tolerance.

Tolerance develops over time, and as a person's tolerance increases, he or she seems less affected by the same amount of alcohol, requiring larger doses to show the behavioral and subjective effects previously experienced with fewer drinks.

In everyday language, a high tolerance for alcohol is referred to as "being able to hold your liquor." Contrary to popular belief, however, tolerance is not a sign that the person can drink safely. Quite to the contrary.

Continued - see source article [pdf]