Why does shaking occur when you withdraw from alcohol?

Answer 1

Heavy alcohol use accustoms the brain and the rest of the central nervous system (CNS) to functioning with alcohol present. That is what addiction is. The body becomes unable to function anywhere close to normally without the drug, and all sorts of things happen when it is withdrawn.

Alcohol's primary effect is central nervous system depression. With repeated heavy consumption of alcohol, certain chemical receptors in the brain (GABAa receptors) are desensitized and reduced in number. The absence of GABA is what causes the CNS depression. When alcohol is stopped, especially abruptly, the person's nervous system suffers from uncontrolled synapse firing because there is not enough GABA to control it. This causes the shakes, and can result in anxiety, life threatening seizures, delirium tremens and hallucinations and possible heart failure.