Not so sure on that. We may have a 'Chicken-n-egg' argument at play here.
Was he mental because of drugs, or did he take drugs in excess because he was mental?
I don't have the answer to that, perhaps you do.
He was way too old for the self-medication with drugs and alcohol excuse. I may sound harsh, but I am old enough to have lived before the Sex, Drugs & Rock’n’Roll revolution, and could see the difference in what people suddenly believed they were entitled to do once hallucenogens and cocaine hit the scene. If you have mental health issues, you still must choose — to fight and win or to give in. He gave in. Many, many times — too many to count. He harmed his children. Just wrong.