How Can ADHD Be Treated?

I have a son, age 45. He had problems in school with not getting homework, etc. and as he became a teenager, he drank alcohol, used some drugs, without my acknolagement, when it was done! In college it even got worse, with the abusment of drugs and booze. He always starts things like classes with loans, really going to do class this time , but just doesn t finish. He can talk to you, and you think he really is going to do what he says this time, he starts, never finish. He just got his drivers license back in November. Got picked up for drinking again. He has been in many classes, nothing helps. He only told me about being told he had adhd about 3or 4 years ago. I thought he was just with the wrong crowd when he was younger, didn t know anything was wrong. I want to know how he can get help for the ADHD.