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.[1] 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.[2][3][4] 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[clarification needed] are the greatest predictors of relapse.[5]
Effects by dosage
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The definition of a unit of alcohol ranges between 8 and 14 grams of pure ethanol depending on the country.[6] 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.[7] 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.[8]
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.