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Alcohol and the body

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What alcohol does to the body

Central nervous system depressant

Drinkers often perceive alcohol to be stimulating. This perception, which usually occurs at lower levels of alcohol intake, results from a depression of inhibitory control mechanisms in the brain. Alcohol, like other general anesthetics, is a primary and continuous depressant of the central nervous system (CNS). First it destroys the integrating control of the brain. Thought processes may be jumbled and disorganized; the drinker may become confused. In addition, motor functions may be disrupted.

Uncontrolled mood swings

The first mental processes to be affected are those that depend on training and experience. The finer grades of discrimination, memory, judgment, concentration and insight will be dulled, then lost.

Confidence may abound. Personality changes may occur as well as uncontrolled mood swings. Emotional outbursts may become frequent. The subject may suffer sensory and motor disturbances. As intoxication progresses, general impairment of nervous function and a condition of general anesthesia prevail.

Factors governing effect of alcohol

The effect of a given amount of alcohol on a person is a function, among other things, of the rate at which the alcohol is consumed, the BAC achieved, the subject's tolerance to alcohol, and the setting (e.g., party atmosphere versus a more sombre setting).

The degree of impairment is dose related. However, it is not identical or linear for all behaviors. It is clear that behavioral skills requiring cognitive functioning suffer the greatest impairment. Put another way, impairment of the cognitive functions begins at lower levels than for simple tasks.

Alcohol tolerance

Tolerance will develop in regular drinkers, but not necessarily uniformly for all behavioral skills. Motor co-ordination shows the most tolerance. Whether tolerance develops with respect to complex skills and cognitive functioning is unclear.

Impairment of divided attention skills (performance of two or more tasks) shows little evidence of tolerance, whereas some short-term memory studies suggest that it may develop for complex tasks, as well as simple ones.

More alcohol needed to achieve same effect

Tolerance to many effects of alcohol is easily developed.

Alcohol is metabolized by the liver. A person who uses alcohol wants the desired effect to last as long as possible. Alcohol metabolism or transformation limits its duration of action.

Repeated exposure of the metabolizing system (mainly the liver) to alcohol increases the system's capability and efficiency. As a result, the alcohol is metabolized more quickly and the duration and intensity of the desired effect are considerably reduced. This is called metabolic tolerance.

To regain the desired effect of the alcohol, the individual must increase the dosage and/or frequency of consumption.

Central nervous system tolerance

CNS tolerance occurs when cells adapt to the presence of alcohol so as to diminish the effect on them of a given level of alcohol. This tolerance does not develop at the same rate for all effects and may not develop at all for others. This is called functional tolerance. As with metabolic tolerance, the user increases the dose and/or frequency of administration to overcome this tolerance, reinstating or enhancing the desired effect.

Loss of tolerance

As with drugs, tolerance to alcohol, once developed, will lessen with time if alcohol is no longer taken regularly. Generally, if drinking stops, the person's body will revert to the tolerance level in existence when alcohol was consumed for the first time. If, after a long period of abstinence, alcohol consumption again becomes regular, there is considerable evidence to suggest the former tolerance is acquired more quickly.

Impairment versus intoxication

It should be noted that individuals can be impaired by alcohol without displaying any outward signs. Impairment is not simply the appearance of gross physical symptoms but it is also a deterioration of judgment, attention, loss of fine co-ordination and control with a possible increase in reaction time and a diminishing of sensory perception.

Intoxication is an advanced state of impairment in which the gross physical symptoms of the effects of alcohol are apparent. The point at which "impairment" becomes "intoxication" is unique to the subject and depends on tolerance.

Impairment and rising or falling BAC

Studies have shown that impairment is greater at a given blood alcohol level when BAC is increasing than for the same BAC when the blood alcohol level is falling. This is called the Mellanby effect.

The manner of consumption also can affect impairment. If alcohol is consumed at a slow and steady pace, it is likely that there will be a slow and steady increase in impairment. If the alcohol is consumed more quickly, the rate of increase in impairment may also be more rapid and appear at lower BACs.

Bolus drinking

If alcohol is consumed quickly (bolus drinking), the rate of performance deficit may be further accelerated because the alcohol is absorbed into the blood stream more rapidly. The increasing impairment is generally obvious to the observer due to the greater than expected rate of deterioration in abilities and performance.

Tolerance developed to a given BAC achieved in social drinking, may not help to moderate the effects of alcohol when the same BAC is achieved by bolus consumption.



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Disclaimer: The material on this site is not intended as legal advice. It merely conveys general information on legal issues commonly encountered by persons facing criminal charges in Canada. If you are charged with an offence, you should contact a criminal lawyer.


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in defence of serious road crimes including impaired driving and dangerous driving.

Office address: 3200 Dufferin Street, Suite 504, Toronto, Ontario
M6A 3B2, Canada.
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Article Contents
1 Introduction
2 What the body does to alcohol
3 Calculations using blood alcohol curve
4 Information for alcohol reports
5 What alcohol does to the body
6 Alcohol and driving