The short-term effects of alcohol consumption range from a decrease in anxiety and motor skills and euphoria at lower doses to intoxication (drunkenness), to stupor, unconsciousness, anterograde amnesia (memory "blackouts"), and central nervous system depression at higher doses. Cell membranes are highly permeable to alcohol, so once it is in the bloodstream, it can diffuse into nearly every cell in the body.
The concentration of alcohol in blood is measured via blood alcohol content (BAC). The amount and circumstances of consumption play a large role in determining the extent of intoxication; for example, eating a heavy meal before alcohol consumption causes alcohol to absorb more slowly. The amount of alcohol consumed largely determines the extent of hangovers, although hydration also plays a role. After excessive drinking, stupor and unconsciousness can both occur. Extreme levels of consumption can cause alcohol poisoning and death; a concentration in the blood stream of 0.36% will kill half of those affected. Alcohol may also cause death indirectly by asphyxiation, caused from vomiting.
Alcohol can greatly exacerbate sleep problems. During abstinence, residual disruptions in sleep regularity and sleep patterns are the greatest predictors of relapse.
Effects by dosage The definition of a unit of alcohol ranges between 8 and 14 grams of pure ethanol depending on the country. There is no agreement on definitions of a low, moderate or high dose of alcohol either. The U.S. National Institute on Alcohol Abuse and Alcoholism defines a moderate dose as alcohol intake up to two standard drinks or 28 grams for men and one standard drink or 14 grams for women. The immediate effect of alcohol depends on the drinker's blood alcohol concentration (BAC). BAC can be different for each person depending on their age, sex, pre-existing health condition, even if they drink the same amount of alcohol.
Different BACs have different effects. The following lists describe the common effects of alcohol on the body depending on the BAC. However, tolerance varies considerably between individuals, as does individual response to a given dosage; the effects of alcohol differ widely between people. Hence in this context, BAC percentages are just estimates used for illustrative purposes.
+ Progressive effects of alcoholA hybridizing of effects as described at and BAC (% by vol.)SI units (mM)mg/dL Behavior Impairment 0.001–0.0290.22–6.31–29 May appear normal Subtle effects detected with special tests 0.030–0.0596.5–12.830–59 Decreased social inhibition Joyousness Mild euphoria Relaxation Increased verbosity Decreased attentional control 0.060–0.09913.0–21.560–99 Alcohol flush reaction Reduced affect display Disinhibition Euphoria Extraversion Increased pain tolerance Depth perception Glare recovery Peripheral vision Reasoning 0.100–0.19921.7–43.3100–199 Analgesia Ataxia Boisterousness Over-expressed emotions Possibility of nausea and vomiting Spins Gross motor skill Motor planning Reflexes Slurred speech Staggering Temporary erectile dysfunction 0.200–0.29943.4–64.9200–299 Anger or sadness Anterograde amnesia Impaired sensations Inhibited sexual desire (ISD) Mood swings Nausea Partial loss of understanding Possibility of stupor Vomiting Amnesia (memory blackout) Unconsciousness Severe physical disability 0.300–0.39965.1–86.6300–399 Central nervous system depression Lapses in and out of consciousness Loss of understanding Low possibility of death Pulmonary aspiration Stupor Dysequilibrium Breathing Resting heart rate Urinary incontinence 0.400–0.50086.80–108.5400–500 Coma Possibility of death Severe central nervous system depression Respiratory failure Heart rate Positional alcohol nystagmus >0.50>108.5>500 High possibility of death
Effects on driving
Research shows an exponential increase of the relative risk for a crash with a linear increase of BAC. NHTSA reports that the following blood alcohol levels (BAC) in a driver will have the following predictable effects on his or her ability to drive safely: (1) A BAC of .02 will result in a "[d]ecline in visual functions (rapid tracking of a moving target), a decline in the ability to perform two tasks at the same time (divided attention)"; (2) A BAC of .05 will result in "[r]educed coordination, reduced ability to track moving objects, difficulty steering, reduced response to emergency driving situations"; (3) A BAC of .08 will result in "[c]oncentration, short-term memory loss, speed control, reduced information processing capability (e.g., signal detection, visual search), impaired perception"; (4) A BAC of .10 will result in "[r]educed ability to maintain lane position and brake appropriately"; and (5) A BAC of .15 will result in "[s]ubstantial impairment in vehicle control, attention to driving task, and in necessary visual and auditory information processing."
Moderate doses Ethanol inhibits the ability of glutamate to open the cation channel associated with the N-methyl--aspartate (NMDA) subtype of glutamate receptors. Stimulated areas include the cortex, hippocampus, and nucleus accumbens, which are all responsible for both thinking and pleasure seeking. Another one of alcohol's agreeable effects is body relaxation, which is possibly caused by neurons transmitting electrical signals in an alpha waves-pattern; such waves are actually observed (with the aid of EEGs) whenever the body is relaxed.
Short-term effects of alcohol include the risk of injuries, violence, and fetal damage. Alcohol alters platelet response; moderate alcohol consumption can increase the amount of time bleeding by slowing down coagulation (as platelet aggregation decreases). Moreover, heavy alcohol consumption can lead to increased platelet aggregation thus increasing blood clotting and possibly leading to strokes and/or thrombosis. Alcohol has also been linked with lowered inhibitions, although it is unclear as to what degree this is chemical or psychological as studies with placebos can often duplicate the social effects of alcohol at either low or moderate doses. Some studies have suggested that intoxicated people have much greater control over their behavior than is generally recognized, though they have a reduced ability to evaluate the consequences of their behavior. Behavioral changes associated with drunkenness are, to some degree, contextual.
A related effect, which is caused by even low levels of alcohol, is the tendency for people to become more animated in speech and movement. This is caused by increased metabolism in areas of the brain associated with movement, such as the nigrostriatal pathway. This causes reward systems in the brain to become more active, which may induce certain individuals to behave in an uncharacteristically loud and cheerful manner.
Alcohol has been known to mitigate the production of antidiuretic hormone, which is a hormone that acts on the kidney to favor water reabsorption in the kidneys during filtration. This occurs because alcohol confuses osmoreceptors in the hypothalamus, which relay osmotic pressure information to the posterior pituitary, the site of antidiuretic hormone release. Alcohol causes the osmoreceptors to signal that there is low osmotic pressure in the blood, which triggers an inhibition of the antidiuretic hormone. As a consequence, one's kidneys are no longer able to reabsorb as much water as they should be absorbing, therefore creating excessive volumes of urine and the subsequent overall dehydration.
Excessive doses and overdose
Symptoms of ethanol overdose may include nausea, vomiting, CNS depression, coma, acute respiratory failure, or death. Levels of even less than 0.1% can cause intoxication, with unconsciousness often occurring at 0.3–0.4%. Death from ethanol consumption is possible when blood alcohol levels reach 0.4%. A blood level of 0.5% or more is commonly fatal. The oral median lethal dose (LD50) of ethanol in rats is 5,628 mg/kg. Directly translated to human beings, this would mean that if a person who weighs drank a glass of pure ethanol, they would theoretically have a 50% risk of dying.
Acute alcohol intoxication through excessive doses in general causes short- or long-term health effects. NMDA receptors become unresponsive, slowing areas of the brain for which they are responsible. Contributing to this effect is the activity that alcohol induces in the gamma-aminobutyric acid (GABA) system. The GABA system is known to inhibit activity in the brain. GABA could also be responsible for causing the memory impairment that many people experience. It has been asserted that GABA signals interfere with both the registration and the consolidation stages of memory formation. As the GABA system is found in the hippocampus (among other areas in the CNS), which is thought to play a large role in memory formation, this is thought to be possible.
Anterograde amnesia, colloquially referred to as "blacking out", is another symptom of heavy drinking. This is the loss of memory during and after an episode of drinking.
Another classic finding of alcohol intoxication is ataxia, in its appendicular, gait, and truncal forms. Appendicular ataxia results in jerky, uncoordinated movements of the limbs, as if each muscle were working independently from the others. Truncal ataxia results in postural instability; gait instability is manifested as a disorderly, wide-based gait with inconsistent foot positioning. Ataxia causes the observation that drunk people are clumsy, sway back and forth, and often fall down. It is presumed to be due to alcohol's effect on the cerebellum.
Mellanby effect The Mellanby effect is the phenomenon that the behavioral impairment due to alcohol is less, at the same BAC, when the BAC is decreasing than when it is increasing. This effect was confirmed in a 2017 meta-analysis.
Effect on different population Based on sex Alcohol affects males and females differently because of difference in body fat percentage and water content. On average, for equal body weight, women have a higher body fat percentage than men. Since alcohol is absorbed into body water content, and men have more water in their bodies than women, for women there will be a higher blood alcohol concentration from the same amount of alcohol consumption. Women are also thought to have less alcohol dehydrogenase (ADH) enzyme which is required to break down alcohol. That is why the drinking guidelines are different for men and women.
Based on genetic variation Alcohol metabolism depends on the enzymes alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). Genetic variants of the genes coding for these enzymes can affect the rate of alcohol metabolism. Some ADH gene variants lead to higher metabolic activity, resulting in the accumulation of acetaldehyde, whereas, a null allele in ALDH2 causes an accumulation of acetaldehyde by preventing its catabolism to acetate. The genetic variants of these enzymes can explain the differences in the alcohol metabolism in different races. The different isoforms of ADH showed protection against alcoholic disorders in Han Chinese and Japanese (due to presence of ADH1B*2 ) and in African (due to presence of ADH1B*3). On the other hand, presence of ALDH2*2 in East Asians (a variant of the ALDH gene), can cause blood acetaldehyde levels of 30 to 75 μM or higher, which is more than 10 times the normal level. The excess amount of blood aldehyde produce facial flushing, nausea, rapid heartbeat, and other adverse effects. Presence of these alleles causes rapid conversion of alcohol to acetaldehyde which can be toxic in large amount. So, the East Asians and Africans feel the adverse effects of alcohol early and stop drinking. For Caucasians, ADH1B*1 allele is the most prevalent allele which causes slower conversion of alcohol to acetaldehyde and it makes them more vulnerable to alcohol use disorders.
Alcohol tolerance