Schizophrenia and drinking beer

My son is 33 years old. He has schizophrenia and he drinks 4-8 beers a night and then at midnight takes his medication. I can deal with the mental illness. I have taught family to family classes and had a support group in the past, but, I can't deal with the drinking. He doesn't get mean or anything, he just starts talking to everyone around him and saying things that doesn't make sense. I have dealt with his illness since 1996, and I am just tired and worn thin. I do not have any other help, his 2 sisters try to avoid him, his dad is not of any help whatsoever. His dad says he drinks to get rid of the voices. When I ask my son why he drinks he says because he likes the taste.  On weekends when he has his 10 yr. old daughter, he doesn't drink at all, but, Sun. night it's a 8-9 beer night. I am frustrated and he doesn't want me to talk to him about it.  He says he enjoys it and he is ok, that he doesn't have a problem. His Dr. has told him he should not drink, but he does anyway. I have been to alenon also. His mental illness is very well controlled when he is not drinking. Yes, he takes his medication as prescribed without a problem.  Help with any suggestions would be appreciated.