Why do most persons with a drug or alcohol problem think they don't have a problem?

There is a one word answer to this question: Denial, but a word that need many words to explain. Basically, the alcoholic or addict has unknowingly developed a lot of mental defenses to avoid recognizing he/she has a problem. Some of these defenses are called rationalization, justification, minimization, externalization, and have definitions that match what they sound like. The alcoholic's and addict's basic drive is to defend the right to continue using. The rationalizing, justifying, and other defenses are all aimed at not having to admit the need to stop using. You can see, I hope, how powerful addiction really is. The more intelligent you are, the more sophisticated your denial system.