Effects of alcohol on the body

The effects of alcohol on the human body can take several forms.

Alcohol, specifically ethanol, is a potent central nervous system depressant, with a range of side effects. The amount and circumstances of consumption play a large part in determining the extent of intoxication; e.g., consuming alcohol after a heavy meal is less likely to produce visible signs of intoxication than consumption on an empty stomach. Hydration also plays a role, especially in determining the extent of hangovers. The concentration of alcohol in blood is usually given by BAC.

Alcohol has a biphasic effect on the body, which is to say that its effects change over time. Initially, alcohol generally produces feelings of relaxation and cheerfulness, but further consumption can lead to blurred vision and coordination problems. Cell membranes are highly permeable to alcohol, so once alcohol is in the bloodstream it can diffuse into nearly every tissue of the body. After excessive drinking, unconsciousness can occur and extreme levels of consumption can lead to alcohol poisoning and death (a concentration in the blood stream of 0.55% will kill half of those affected). Death can also be caused by asphyxiation when vomit, a frequent result of overconsumption, blocks the trachea and the individual is too inebriated to respond. An appropriate first aid response to an unconscious, drunken person is to place them in the recovery position.

Intoxication frequently leads to a lowering of one's inhibitions, and intoxicated people will do things they would not do while sober, often ignoring social, moral, and legal considerations.

Intoxication
Ethanol acts as a central nervous system depressant. In small amounts, ethanol causes a mild euphoria and removes inhibitions, and in large doses it causes drunkenness, generally at a Blood Alcohol Content of about 0.1%. At higher concentrations, alcohol causes intoxication, coma, and death. A blood ethanol content above 0.4% can be fatal, although regular heavy drinkers can tolerate somewhat higher levels than non-drinkers. Eight to ten drinks per hour is considered a fatal dosage for the average 54 kg (119 lb.) person. One drink is equivalent to one shot of 40% abv (80 proof) liquor, one 12 US fl oz (355 ml) beer, or one 4–5 US fl oz (120–150 ml) glass of wine.

In the UK, a "unit" of alcohol is 10 ml pure ethanol; so examples of drinks containing one unit of alcohol include one 25 ml measure of spirits (40% ABV), one 125 ml glass of weak wine (8% ABV), one half-pint (284 ml) of weak (3.5% ABV) beer, or just over one third of a pint (about 200 ml) of "premium" (5% ABV) lager. (Note that in fact most wines are about 12% ABV, so would contain 1.5 units per 125 ml glass, and that many establishments serve wine by the 175 ml glass. A 175ml glass of 12% wine contains 2.1 units of alcohol).

To determine how many units an alcoholic drink contains a simple formula may be used:

(ABV*ml)/1000

Thus, a "shot" of 40% ABV liquor in the US (approximately 44ml or 1.5 US fl oz) is actually 1.76 units of alcohol ((40*44)/1000). As a result, one U.S. "shot" of alcohol is almost double the amount experienced by the international community. As a result, "shot-takers" in the United States should be aware of the differences between the two standards and adjust accordingly to prevent alcohol overconsumption. Alcoholism, addiction to alcohol, is a major public health problem. Alcoholics develop a number of health problems, with cirrhosis of the liver among the most significant. Unlike withdrawal from some other drugs/intoxicants such as the opioids, withdrawal from heavy alcohol consumption can produce delirium tremens that can be fatal.

Any alcohol consumption during pregnancy carries a heavy risk of permanent mental and physical defects in the child, known as fetal alcohol spectrum disorder.

Action on the brain
Ethanol is quickly absorbed into the bloodstream and reaches the brain. As a small molecule, it is able to cross the blood-brain barrier. The molecular targets of alcohols actions remain essentially unidentified, although many targets have been suggested, including ion channels and intracellular signaling molecules. Alcohol works on the GABA system at the synaptic level, and it has a rapid onset of action. Essentially, it causes the GABA receptor, which is an ion channel, to remain open longer than it does without the addition of ethanol into the synaptic cleft (the space between two neurons, or brain cells). This causes more negatively charged particles to enter brain cells than would under normal conditions. The overall effect is to slow the functional processes of the brain cell. GABA is commonly known as the brain's "brake" mechanism.

Blackouts
"Blacking out" or blackouts (a form of anterograde amnesia) are a common problem usually associated with heavy drinking. They are characterized by a person's inability to recall events which occurred during the period of blacking out. Blackouts can be avoided or prevented by drinking less, drinking water and eating. A 2001 survey at Duke University found that 7.1% of respondents had experienced blackouts within 2 weeks of the survey. 

Carcinogenic effects
The International Agency for Research on Cancer (Centre International de Recherche sur le Cancer) of the World Health Organization has classified alcohol as a Group 1 carcinogen. Its evaluation states, "There is sufficient evidence for the carcinogenicity of alcoholic beverages in humans.… Alcoholic beverages are carcinogenic to humans (Group 1)."

The U.S. National Institute on Alcohol Abuse and Alcoholism (NIAAA) reports that "Although there is no evidence that alcohol itself is a carcinogen, alcohol may act as a cocarcinogen by enhancing the carcinogenic effects of other chemicals. For example, studies indicate that alcohol enhances tobacco's ability to stimulate tumor formation in rats.  In humans, the risk for mouth, tracheal, and esophageal cancer is 35 times greater for people who both smoke and drink than for people who neither smoke nor drink,  implying a cocarcinogenic interaction between alcohol and tobacco-related carcinogens."

"Studies have suggested that high concentrations of acetaldehyde, which is produced as the body breaks down ethanol, could damage DNA in healthy cells. … Researchers at the National Institute on Alcohol Abuse and Alcoholism in Bethesda, Maryland, have added weight to this idea by showing that the damage occurs at concentrations of acetaldehyde similar to those in saliva and the gastrointestinal tract while people drink alcohol. Acetaldehyde appears to react with polyamines - naturally occurring compounds essential for cell growth - to create a particularly dangerous type of mutagenic DNA base called a Cr-Pdg adduct…"

The strongest link between alcohol and cancer involves cancers of the upper digestive tract, including the esophagus, the mouth, the pharynx, and the larynx. Less consistent data link alcohol consumption and cancers of the liver, breast, and colon.

Upper digestive tract. Chronic heavy drinkers have a higher incidence of esophageal cancer than does the general population. The risk appears to increase as alcohol consumption increases. An estimated 75% of esophageal cancers in the United States are attributable to chronic, excessive alcohol consumption.

Nearly 50% of cancers of the mouth, pharynx, and larynx are associated with heavy drinking. According to mid-1980s U.S. case-control study, people who consumed an average of more than four drinks per day incurred a nine-fold increase in risk of oral and pharyngeal cancer, while there was about a four-fold increase in risk associated with smoking two or more packs of cigarettes per day. Heavy drinkers who also were heavy smokers experienced a greater than 36-fold excess compared to abstainers from both products.

Liver. Prolonged, heavy drinking has been associated in many cases with primary liver cancer. However, it is liver cirrhosis, whether caused by alcohol or another factor, that is thought to induce the cancer. In the United States, liver cancer is relatively uncommon, afflicting approximately 2 people per 100,000, but excessive alcohol consumption is linked to as many as 36% of these cases by some investigators.

Metabolism of alcohol and action on the liver
The liver breaks down alcohols into acetaldehyde by the enzyme alcohol dehydrogenase, and then into acetic acid by the enzyme acetaldehyde dehydrogenase. Next, the acetate is converted into fats or carbon dioxide and water. The fats are mostly deposited locally which, according to some, leads to the characteristic "beer belly". Chronic drinkers, however, so tax this metabolic pathway that things go awry: fatty acids build up as plaques in the capillaries around liver cells and those cells begin to die, which leads to the liver disease cirrhosis. The liver is part of the body's filtration system and if it is damaged then certain toxins build up, thus leading to symptoms of jaundice.

The alcohol dehydrogenase of women is less effective than that of men. The percentage of water in women's bodies is less than that of men. Therefore, the alcohol has less volume to dissolve in, leading to a higher blood alcohol concentration when the same amount of alcohol is ingested. This contributes to the fact that women become intoxicated more quickly than men. Also contributing is the fact that men have a more active first-pass metabolism of alcohol in the stomach and small intestine.

Some people, especially those of East Asian descent, have a genetic mutation in their acetaldehyde dehydrogenase gene, resulting in less potent acetaldehyde dehydrogenase. This leads to a buildup of acetaldehyde after alcohol consumption, causing the alcohol flush reaction with hangover-like symptoms such as flushing, nausea, and dizziness. These people are unable to drink much alcohol before feeling sick, and are therefore less susceptible to alcoholism. , This adverse reaction can be artificially reproduced by drugs such as disulfiram, which are used to treat chronic alcoholism by inducing an acute sensitivity to alcohol.

Dehydration
Consumption of ethanol has a rapid diuretic effect, meaning that more urine than usual is produced, since ethanol inhibits the production of antidiuretic hormone.

Overconsumption can therefore lead to dehydration (the loss of water).

Hangover
A common after-effect of ethanol intoxication is the unpleasant sensation known as hangover, which is partly due to the dehydrating effect of ethanol. Hangover symptoms include dry mouth, headache, nausea, and sensitivity to light and noise. These symptoms are partly due to the toxic acetaldehyde produced from alcohol by alcohol dehydrogenase, and partly due to general dehydration. The dehydration portion of the hangover effect can be mitigated by drinking plenty of water between and after alcoholic drinks. Other components of the hangover are thought to come from the various other chemicals in an alcoholic drink, such as the tannins in red wine, and the results of various metabolic processes of alcohol in the body, but few scientific studies have attempted to verify this. Consuming water between drinks is the best way to prevent or lessen the effects of a hangover.

Beneficial effects of alcohol

 * See also: Alcohol consumption and health

The World Health Organization (WHO) reports that there is convincing evidence that "low to moderate alcohol intake" results in a decreased risk of coronary heart disease. However, the WHO cautions that "other cardiovascular and health risks associated with alcohol do not favour a general recommendation for its use."

Also it has been suggested that moderate consumption of alcohol can reduce the risk of dementia, facilitate memory and learning, and even improve IQ scores. Moderate drinkers tend to have better health and live longer than those who abstain from alcohol or are heavy drinkers.

Effects by dose
Different concentrations of alcohol in the human body have different effects on the subject. The following lists the effects of alcohol on the body, depending on the blood alcohol concentration or BAC. For further references, refer:  and.


 * Please note: the BAC percentages provided below are just estimates and used for illustrative purposes only. They are not meant to be an exhaustive reference; please refer to a healthcare professional if more information is needed.


 * Euphoria (BAC = 0.03 to 0.12 %)
 * Subject may experience an overall improvement in mood and possible euphoria.
 * They may become more self-confident or daring.
 * Their attention span shortens. They may look flushed.
 * Their judgement is not as good — they may express the first thought that comes to mind, rather than an appropriate comment for the given situation.
 * They have trouble with fine movements, such as writing or signing their name.


 * Lethargy (BAC = 0.09 to 0.25 %)
 * Subject may become sleepy
 * They have trouble understanding or remembering things, even recent events. They do not react to situations as quickly.
 * Their body movements are uncoordinated; they begin to lose their balance easily, stumbling; walking is not stable.)
 * Their vision becomes blurry. They may have trouble sensing things (hearing, tasting, feeling, etc.).


 * Confusion (BAC = 0.18 to 0.30 %)
 * Profound confusion — uncertain where they are or what they are doing. Dizziness and staggering occur.
 * Heightened emotional state — aggressive, withdrawn, or overly affectionate. Vision, speech, and awareness are impaired.
 * Poor coordination and pain response. Nausea and vomiting often occur.


 * Stupor (BAC = 0.25 to 0.40 %)
 * Movement severely impaired; lapses in and out of consciousness.
 * Subjects can slip into a coma; will become completely unaware of surroundings, time passage, and actions.
 * Risk of death is very high due to alcohol poisoning and/or pulmonary aspiration of vomit while unconscious.


 * Coma (BAC = 0.35 to 0.50 %)
 * Unconsciousness sets in.
 * Reflexes are depressed (i.e., pupils do not respond appropriately to changes in light).
 * Breathing is slower and more shallow. Heart rate drops. Death usually occurs at levels in this range.


 * Death (BAC more than 0.50 %)
 * Alcohol causes central nervous system to fail, resulting in death.

Moderate doses
Although alcohol is typically thought of purely as a depressant, at low concentrations it can actually stimulate certain areas of the brain. Alcohol sensitises the N-methyl-D-aspartate (NMDA) system of the brain, making it more receptive to the neurotransmitter glutamate. Stimulated areas include the cortex, hippocampus and nucleus accumbens, which are responsible for thinking and pleasure seeking. Another one of alcohol's agreeable effects is body relaxation, possibly caused by heightened alpha brain waves surging across the brain. Alpha waves are observed (with the aid of EEGs) when the body is relaxed. Heightened pulses are thought to correspond to higher levels of enjoyment.

A well-known side effect of alcohol is lowering inhibitions. Areas of the brain responsible for planning and motor learning are dulled. A related effect, caused by even low levels of alcohol, is the tendency for people to become more animated in speech and movement. This is due to 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, and combined with reduced understanding of the consequences of their behavior, can induce people to behave in an uncharacteristically loud and cheerful manner.

Behavioural changes associated with drunkenness are, to some degree, contextual. A scientific study found that people drinking in a social setting significantly and dramatically altered their behaviour immediately after the first sip of alcohol, well before the chemical itself could have filtered through to the nervous system. Likewise, people consuming non-alcoholic drinks often exhibit drunk-like behaviour on a par with their alcohol-drinking companions even though their own drinks contained no alcohol whatsoever.

Excessive doses
The effect alcohol has on the NMDA receptors, earlier responsible for pleasurable stimulation, turns from a blessing to a curse if too much alcohol is consumed. NMDA receptors start to become unresponsive, slowing thought in the areas of the brain they are responsible for. Contributing to this effect is the activity which alcohol induces in the gamma-aminobutyric acid system (GABA). The GABA system is known to inhibit activity in the brain. GABA could also be responsible for the memory impairment that many people experience. It has been asserted that GABA signals interfere with the registration and 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.

Blurred vision is another common symptom of drunkenness. Alcohol seems to suppress the metabolism of glucose in the brain. The occipital lobe, the part of the brain responsible for receiving visual inputs, has been found to become especially impaired, consuming 29 % less glucose than it should. With less glucose metabolism, it is thought that the cells aren't able to process images properly.

Often, after much alcohol has been consumed, it is possible to experience vertigo, the sense that the room is spinning (referred to in certain circles as 'The Spins'). This is associated with abnormal eye movements called nystagmus, specifically positional alcohol nystagmus. In this case, alcohol has affected the organs responsible for balance (vestibular system), present in the ears. Balance in the body is monitored principally by two systems: the semicircular canals, and the utricle and saccule pair. Inside both of these is a flexible blob called a cupula, which moves when the body moves. This brushes against hairs in the ear, creating nerve impulses that travel through the vestibulocochlear nerve (Cranial nerve VIII) in to the brain. However, when alcohol gets in to the bloodstream it distorts the shape of the cupola, causing it to keep pressing on to the hairs. The abnormal nerve impulses tell the brain that the body is rotating, causing disorientation and making the eyes spin round to compensate. When this wears off (usually taking until the following morning) the brain has adjusted to the spinning, and interprets not spinning as spinning in the opposite direction causing further disorientation. This is often a common symptom of the hangover.

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 though 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 is responsible for the observation that drunk people are clumsy, sway back and forth, and often fall down. It is probably due to alcohol's effect on the cerebellum.

Extreme overdoses can lead to alcohol poisoning and death due to respiratory depression.

A rare complication of acute alcohol ingestion is Wernicke encephalopathy, a disorder of thiamine metabolism. If not treated with thiamine, Wernicke encephalopathy can progress to Korsakoff psychosis, which is irreversible.

Chronic alcohol ingestion over many years can produce atrophy of the vermis, which is the part of the cerebellum responsible for coordinating gait; vermian atrophy produces the classic gait findings of alcohol intoxication even when its victim is not inebriated.

Severe drunkenness and diabetic coma can be mistaken for each other on casual inspection, with potentially serious medical consequences for diabetics. The major physical finding they share is the sickly-sweet odour of ketosis on the breath; alcoholic ketosis and diabetic ketosis are both marked by the presence of acetone and other ketones in the bloodstream, although the ketones are produced by different metabolic pathways in each disorder. Measurement of the serum glucose and ethanol concentrations in comatose individuals is routinely performed in the emergency department and easily distinguishes the two conditions.