How Alcohol Works :
Alcohol- is rapidly absorbed into the bloodstream from the small intestine, and less rapidly from the stomach and colon. In proportion to its concentration in the bloodstream, alcohol decreases activity in parts of the brain and spinal cord. The drinker's blood alcohol concentration depends on:

    * the amount consumed in a given time
    * the drinker's size, sex, body build, and metabolism
    * the type and amount of food in the stomach.

Once the alcohol has passed into the blood, however, no food or beverage can retard or interfere with its effects. Fruit sugar, however, in some cases can shorten the duration of alcohol's effect by speeding up its elimination from the blood.

In the average adult, the rate of metabolism is about 8.5 g of alcohol per hour (i.e. about two-thirds of a regular beer or about 30 mL of spirits an hour). This rate can vary dramatically among individuals, however, depending on such diverse factors as usual amount of drinking, physique, sex, liver size, and genetic factors.
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It is the amount of alcohol in the blood that causes the effects. In the following table, the left-hand column lists the number of milligrams of alcohol in each decilitre of blood - that is, the blood alcohol concentration, or BAC. (For example, an average person may get a blood alcohol concentration of 50 mg/dL after two drinks consumed quickly.) The right-hand column describes the usual effects of these amounts on normal people - those who haven't developed a tolerance to alcohol.

BAC
(ma/dL) Effect
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50  Mild intoxication
    Feeling of warmth, skin flushed; impaired judgment;
    decreased inhibitions


100  Obvious intoxication in most people
    Increased impairment of judgment, inhibition, attention, and control;
    Some impairment of muscular performance; slowing of reflexes


150  Obvious intoxication in all normal people
    Staggering gait and other muscular incoordination; slurred
    speech; double vision; memory and comprehension loss


250  Extreme intoxication or stupor
    Reduced response to stimuli; inability to stand; vomiting;
    incontinence; sleepiness

350  Coma
    Unconsciousness; little response to stimuli; incontinence;
    low body temperature; poor respiration; fall in blood
    pressure; clammy skin

500  Death likely
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Source: http://www.erowid.org/chemicals/alcohol/alcohol_info2.shtml