Alcohol Use Disorder involves problematic alcohol use with tolerance, withdrawal, unsuccessful cut-down attempts, and continued use despite harm. Alcohol is a CNS depressant affecting GABAergic and glutamatergic systems; chronic use causes neuroadaptations producing withdrawal syndrome (tremor, seizures, delirium tremens in severe cases). AUD has significant medical consequences (liver cirrhosis, cardiomyopathy, neuropathy) and major psychosocial impacts.
From your study of substance use disorders, you know that the defining features of addiction involve tolerance, withdrawal, loss of control, and continued use despite negative consequences. Alcohol Use Disorder (AUD) exemplifies this pattern, but its specific neurochemical mechanisms differ from stimulants or opioids — understanding those mechanisms explains why alcohol withdrawal can be medically dangerous in a way that opioid withdrawal typically is not.
Alcohol is a positive allosteric modulator of GABA-A receptors and an antagonist at NMDA glutamate receptors. In plain terms, it amplifies the brain's main inhibitory signal (GABA) and suppresses the main excitatory signal (glutamate). The immediate effect is sedation, anxiolysis, and the loosened social inhibition characteristic of mild intoxication. Over time, the brain adapts to compensate: GABA-A receptors are downregulated (fewer receptors, reduced sensitivity) and NMDA receptors are upregulated (more receptors, increased sensitivity). The nervous system re-establishes a functional equilibrium, but it is now calibrated to expect constant alcoholic input.
When alcohol is abruptly removed, this compensatory adaptation is suddenly unmasked. Without alcohol dampening GABA activity, the now-reduced GABA system cannot adequately inhibit the now-upregulated NMDA-driven excitation. The result is CNS hyperexcitability: tremor within hours, then insomnia, sweating, and autonomic instability, progressing in severe cases to seizures (at 6–48 hours) and delirium tremens (48–96 hours) — a life-threatening state of confusion, hallucinations, and severe autonomic dysregulation. This is why alcohol withdrawal is treated with benzodiazepines, which substitute for alcohol's GABAergic effect, allowing the brain to be gradually tapered rather than abruptly deprived.
The medical consequences of chronic heavy drinking extend far beyond the CNS. The liver, which metabolizes roughly 80% of ingested alcohol via alcohol dehydrogenase, bears the greatest burden: fatty liver progresses to alcoholic hepatitis and eventually cirrhosis (irreversible scarring), which impairs clotting factor synthesis, bile production, and toxin clearance. Direct cardiotoxicity produces alcoholic cardiomyopathy (dilated, weakened heart muscle). Peripheral neuropathy — pain, numbness, weakness in hands and feet — results from direct toxic effects on axons and thiamine (B1) deficiency. Severe thiamine deficiency produces Wernicke-Korsakoff syndrome, a devastating neurological condition combining acute encephalopathy with permanent amnesia. Understanding these mechanisms helps clinicians prioritize both the immediate treatment of withdrawal (preventing seizures) and the longer-term management of end-organ damage.