The Big Book of Alcoholics Anonymous: Chapter on Medical Opinion

[...] the alcoholic's body is just as sick as their mind. We, alcoholics, fully agree with this. We cannot be satisfied with the explanation that we cannot control our drinking because we adapt poorly to life; or because we flee from reality, or because we are obviously feeble-minded. This may be true to some extent for some of us. Nevertheless, we are convinced that our bodies are also sick. In our view, the picture of the alcoholic is incomplete if it ignores this physical factor.

We became interested in the doctor's theory that we are allergic to alcohol. Since we are not professionals, our opinion on the validity of this theory does not count for much. But as former problem drinkers, we can say that the explanation seems to make sense. It provides a rationale for many things that we otherwise could not explain.

Big Book - Why Do People Drink?

People actually drink because they like the effect that alcohol produces.  
[Alcoholics Anonymous, xxviii]

Big Book - On Alcohol Sensitivity

If the alcoholic refrains from drinking - which can be for months or years - their reactions are largely like those of other people. Likewise, we can be sure that if they consume even a small amount of alcohol, something happens both physically and mentally that makes it practically impossible for them to stop. The experiences of countless alcoholics can provide ample evidence of this.  
[Alcoholics Anonymous, p. 22]

Big Book - On Alcohol Dependency

The Big Book of Alcoholics Anonymous states about alcohol dependency on page 23:  
"Every alcoholic reaches a point in drinking when the strongest desire to stop drinking is of no value. This tragic situation occurs virtually always before they realize it. The fact is that most alcoholics, for reasons yet unknown, lose their ability to make decisions regarding drinking. Their so-called willpower practically ceases to exist. At times, they are unable to vividly recall the painful humiliations they suffered even a week or a month prior. They are defenseless against the first drink. The almost certain consequences that arise from consuming even a single beer do not come to mind to deter them. Even if these thoughts do arise, they are vague and are immediately pushed aside by the clichéd notion that this time they can behave like others. This is where that kind of defense mechanism fails, which prevents a person from putting their hand on the hot stove."

Thus, it is not enough for me to realize that if I don’t drink the first drink, I won’t get drunk. But why did I always drink the first drink before I got to know the AA program? I did so because I couldn’t feel good without alcohol. The first step of the AA program helped me realize that due to my alcohol-sensitive body, I cannot stop after the first drink. However, I needed to take all the other steps to grow spiritually and feel good without alcohol (or any other substance).

It is perhaps no coincidence that someone who is still at the point of taking the steps may feel that their dependency is untreatable, that if they were once dependent, they will always be so, just that they will change substances. Fortunately, this is not true. There is a solution. It is called the 12 Steps.

Big Book - On Alcoholism

Most of us are reluctant to admit that we are true alcoholics. No one likes to think that they differ physically and mentally from their fellow humans. So it is not surprising that our drinking careers are filled with countless futile attempts to prove that we can drink like others. Every abnormal drinker has the obsession that somehow, someday, they will be able to limit and enjoy drinking. It is amazing how stubborn this dream is. Many perhaps drive themselves to the brink of madness or death.

Deep down, we must admit that we are alcoholics. This is the first step toward recovery. We must discard the delusion that we are or soon can be like other people.  
[Alcoholics Anonymous, p. 29 - A Few More Words About Alcoholism]

Big Book - On Drinking in an Alcoholic Manner

We alcoholics have lost our ability to drink in moderation. We know that no true alcoholic ever regains this ability. Occasionally, we all feel that we have regained control, but these - usually short - periods are inevitably followed by even greater excess, leading to a pitiful and inexplicable moral decline. We firmly believe that alcoholics like us suffer from a progressively worsening disease. With every single day that passes, our condition only gets worse; it never gets better.

We are like a person who has lost the ground beneath their feet and cannot stand up again. There is no treatment that can make an alcoholic like us similar to other people. We have tried every conceivable remedy. In some cases, we have achieved temporary improvement, but this has always been followed by an even worse relapse. Doctors familiar with alcoholism agree that no alcoholic can be transformed into a normal drinker. Science may one day achieve this, but it has not reached that point yet.  
[Alcoholics Anonymous, pp. 29-30]

Big Book - On the Hopelessness of Normal Drinking

Most of us think that if we stay sober for a long time, we can drink normally. [...] If someone resumes drinking after a sober period, they will soon find themselves back where they were before. If we plan to stop drinking, we must not think that one day we will become immune to alcohol.  
[Alcoholics Anonymous, p. 31]

Big Book - On Relapse

"Suddenly, it flashed in my mind that if I poured a shot of whiskey into my milk, it wouldn't hurt my full stomach. I ordered a whiskey and poured it into the milk. I vaguely felt that this was not a very smart thing to do, but I was encouraged by the fact that I was drinking the whiskey on a full stomach. The experiment went so well that I ordered another whiskey and poured it into another glass of milk. It seemed that it wouldn’t hurt, so I tried a third one."

Thus began Jim’s new journey to the psychiatric hospital.  
[Alcoholics Anonymous, pp. 34-35]