The mechanism of ethanol intoxication and withdrawal is complex. Most of the clinical effects can be explained by the interaction of ethanol with various neurotransmitters and neuroreceptors in the brain, including those interacting with gamma-aminobutyric acid (GABA), glutamate (NMDA), and opiates.Resulting changes in the inhibitory and excitatory neurotransmitters disrupt the neurochemical balance in the brain, causing symptoms of withdrawal.
In opioid or benzodiazepine addiction, chronic stimulation of specific receptors for these drugs suppresses endogenous production of neurotransmitters (endorphins or GABA, respectively). Removal of exogenous drug allows unopposed counter-regulatory effects to become clinically apparent. When the exogenous drug is precipitously removed, inadequate production of endogenous transmitters and the unopposed stimulation by counter-regulatory transmitters results in the characteristic clinical picture of withdrawal.
Alcohol withdrawal
Withdrawal symptoms appear within 6-12 hours after individuals cease or decrease alcohol intake and are usually relieved by consuming additional alcohol.
The hallmark of alcohol withdrawal is a continuum of signs and symptoms ranging from simple tremulousness to DT.

    * Mild withdrawal usually occurs within 24 hours of the last drink and is characterized by tremulousness (shakes), insomnia, anxiety, hyperreflexia, diaphoresis, mild autonomic hyperactivity, and GI upset.
    * Moderate withdrawal usually occurs 24-36 hours after the cessation of alcohol intake and includes intense anxiety, tremors, insomnia, and excessive adrenergic symptoms.
    * Severe withdrawal usually occurs more than 48 hours after a cessation or decrease in alcohol consumption. It is characterized by profound alteration of sensorium including disorientation, agitation, and hallucinations; along with severe autonomic hyperactivity including tremulousness, tachycardia, tachypnea, hyperthermia, and diaphoresis.
Opioid withdrawal
In general, opioid withdrawal does not directly cause life-threatening symptoms, seizures, or delirium.
Opioid withdrawal syndrome may resemble a severe flu-like illness. The syndrome is characterized by rhinorrhea, sneezing, yawning, lacrimation, abdominal cramping, leg cramping, piloerection, nausea, vomiting, diarrhea, and dilated pupils.

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