There is no single answer. Some people drink alcohol with the express purpose of getting drunk. Some people drink alcohol because they like the taste, and it doesn't matter to them whether they get drunk or not. Some people have just one alcoholic drink because they don't like the idea/feeling of being drunk so they limit themselves to one drink. Some people don't drink alcohol at all because of religious or health reasons.
So - some people drink alcohol in order to get drunk and getting drunk/tipsy is the result of drinking alcohol for many people.
If you tell your friend that you don't want to accept his offer of a glass of wine because wine makes you tipsy, he will think that you have drunk wine before. Why not tell him the truth? Just say that you don't drink wine because you believe it's bad for your prostate.