Tom I'm quite sure many talented artists in almost any field have used drugs and or alcohol as either a stimulant or a crutch. Why would GCA's be an anomaly in this regard. Certainly no one is implying that being an artist of sorts makes you a likely suspect, or is necessary to succeed.
In my youth I caddied for some of the most successful people in the world both in NJ and Florida, getting to know many of them as few would. Most didn't use or drink to excess, but some did.
The smartest guy who I ever met wasn't one of them. He was a local guy who had multiple PH'D's and a terrible addiction problem. I truly believe the world he lived in was just not fast enough. It bored him .He often challenged me on subjects which I thought was outside his wheelhouse and in mine, yet I quickly found he had no such blind spots. He was kind enough to ask me questions he probably knew the answers to better than I. He died from his affliction, and it was a terrible loss for many of us.
I think it was hard for him to live in a world that was so simple for him, and the drugs and alcohol leveled him out. Without them he may not have been able to cope. Mike's query surely isn't too far fetched and indeed has been the predicate of some interesting discussion here on the forum.