This tendency has fascinated me since I started doing comedy back in Melbourne in the early 1990s. Being a total square who only drank a bit of red wine occasionally and didn't indulge in any other drugs, I was certainly in a very small minority.
Culture plays a part
It astonished me how much drug use there was amongst my peers. Dope in particular was a big part of the whole scene. Harder drugs were used on occasion. From time to time you'd hear about how some bloke or other had become hooked on smack, or, hearteningly, had actually managed to kick that particular habit.
I think part of the reason so many are into drugs in comedy is to do with culture. To make jokes about society, you have to be on the outside looking in. Thumbing your nose at normality becomes a running state. You get much material from staying off the straight and narrow. It's easy to see how drugs can easily become part of that process.
This abnormal, or rather anti-normal lifestyle, becomes a kind of norm in itself. Sharing a joint with your fellow comedians is much like having knock off drinks at the local pub, a common ritual for many who work nine to five.
Then there's the fact that comedians, like other creative artists, are flawed people with more issues than most. They are often deeply angry and depressed. These dark inner processes are what fuels their humor. Being so sensitive they find it hard to stay on an even keel and end up self-medicating.
The thrill of performance
And I think there's one element that often gets missed. That's the addictive nature of performing comedy itself. It really is an exhilarating experience. Daring to get up in front of a whole bunch of people and win them over with your presence, delivery and material is an extremely risky thing to attempt. When it works it's a real high, no doubt about it. Each laugh you get gives you a jolt of endorphins. And if you have an exceptionally good gig, well, you're walking on air for hours ...
The kind of person who is drawn to it is often a special kind of adrenaline junkie. He gets hooked on getting laughs! But he can't be doing it every night. So he has to press those buttons in the brain in some other way when he can't get his performance "fix". Hence the use of chemical replacements.
What do you think? Any other reasons so many comics have drug and alcohol issues?