A chemical imbalance
The more complex answer is that when the brain is functioning normally, it has a balance of neurotransmitters which are chemicals that help the brain communicate with the rest of the body. When alcohol is introduced to the mix, it can alter the balance of the chemicals in the brain resulting in fatigue, minimal coordination, and euphoric feelings.
However, when someone continues to drink over long periods of time, their brain becomes accustomed to these chemical imbalances. In turn, small amounts of alcohol no longer have the same effects they once did, meaning people must drink more in order to reach the same state. As the brain continues to adapt to the effects of alcohol, it protests in the form of withdrawals when that alcohol is not present.
Alcohol changes the brain
According to the National Institute on Alcohol Abuse and Alcoholism, “As the brain adapts to alcohol’s presence over time, a heavy drinker may begin to respond to alcohol differently than someone who drinks only moderately. Some of these changes may be behind alcohol’s effects, including alcohol tolerance and alcohol withdrawal symptoms. These effects are associated with alcohol dependence.”
Ultimately, this is the reason an alcoholic continues to drink — to curb these withdrawals and cravings to return the brain to its new normal. Over time, this cycle continues and keeps intensifying, likely until an alcoholic hits their bottom and decides to stop drinking for good.
However, some alcoholics do not always stop drinking for good when they initially quit. Many will relapse, returning to the same lifestyle and alcoholic tenancies they had before quitting. The brain will react the same way, almost welcoming alcohol back into the balance. The severity of the brain’s reaction is dependent upon how much time has passed between drinks, but often it will be as if the brain offers a sigh of relief, and says “welcome back, old friend.”
Each individual is different, but it’s likely that once an alcoholic returns to drinking, they will quickly find themselves in the same circumstances as before they quit the first time.