Basically, i think you have to specify how much drinking or drugs one is doing, before trying to make any kind of correlation between that activity and any form or creative expression, no matter what it might be.
What amazes me is world class musicians who can play. (and apparently play well) when drunk or stoned, or pool players, (or any athletes who seem to get better with the more they drink), because I know personally that my reflexes go to blazes after 4 - 5 drinks.
As far as writing goes however, I've been drinking 3 Beers a night for the last 30 years and haven't noticed any increase or decrease in the frequency or quality of my writing.
As a matter of fact, I find that much of my best writing comes in the middle of the night, (after I've been drinking) when I can't sleep because my mind won't shut down. I used to try and fight it and hope whatever inspiration I was having would still be there in the morning, but, in recent years, I've found myself getting up, going to my computer and writing down what's going through my head, and the result has been a flood of quality Limericks and Haiku that were well worth the loss of sleep.
I can't say any of my major poems have been written that way, (although I have occasionally gotten fragments, and more than a few complete Song Lyrics as a result.).
I have written a couple of drinking songs and poems, but as I remember (for it was many years ago), I was neither drunk nor hungover when I wrote them, but I don't pretend that I'm typical of everybody. The only thing I will say is that it never pays to generalize too much about subjects like this, (anymore than one can generalize about suicidal tendencies and emotional unbalance among poets like Plath and that ilk)
Inspiration comes whenever and wherever and we, who write, can only be glad that it does.
James R. Hoye, (JRH)