Addiction

The brain makes its own opium-like chemicals called encephalins. These are produced in response to pain, and they act on special receptors in the brain and spinal cord. They produce pain relief and a sense of euphoria. Chemicals such as morphine or heroin bind to these same receptors with the same effect.

If the receptors are exposed to the drugs over a period of time, the response changes: the receptors become less effective because the cells reduce their level of activity in response to excessive stimulation. More drug is needed to achieve the same effect. This is TOLERANCE.
If the drug is stopped, the cells become overactive, causing craving. This is DEPENDENCE.
The over activity affects cells other than the receptors, causing withdrawal symptoms of sweating, shaking, nausea, vomiting and diarrhoea.

ALCOHOL does not work on receptors, but acts generally throughout the brain as a suppressor of function, which is why a little acts as a sedative, and a lot produces coma. Alcohol also reduces our blood sugar and acts as a diuretic, causing us to produce excess urine. This means that too much alcohol causes headache and dry mouth - the symptoms of hangover. Over a period of time with repeated exposure the brain adapts, the effects are reduced and tolerance develops.
Withdrawal may produce the symptoms of dependence: craving, nausea and retching and shaking. In severe cases there may be hallucinations and seizures. Chronic alcoholics may develop permanent damage to brain structure by direct toxic effects and by associated vitamin deficiency.
 
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