For example, alcohol initially enhances the effect of GABA, the neurotransmitter which produces feelings of relaxation and calm. But chronic alcohol consumption eventually suppresses GABA activity so that more and more alcohol is required to produce the desired effects, a phenomenon known as tolerance.
Chronic alcohol consumption also suppresses the activity of glutamate, the neurotransmitter which produces feelings of excitability. To maintain equilibrium, the glutamate system responds by functioning at a far higher level than it does in moderate drinkers and nondrinkers.
When heavy drinkers suddenly stop or significantly reduce their alcohol consumption, the neurotransmitters previously suppressed by alcohol are no longer suppressed. They rebound, resulting in a phenomenon known as brain hyperexcitability. So, the effects associated with alcohol withdrawal — anxiety, irritability, agitation, tremors, seizures, and DTs — are the opposite of those associated with alcohol consumption.