Like piles of people said, it's a matter of personal threshold.

Mine for pot is zero or I'm asleep in nothing flat. Losing intonation & co-ordination on alcohol, that's me after the first draught (draft but bigger) so there are 2 rules about booze: no performing after more than one pint at most and no more than one pint at most if I'm performing. Not a problem since I don't like warm beer.

Nicotine I'm thoroughly addicted to, but on stage? While busking? Only on breaks.

Other things I've tried would never make it to stage: caffeine, cocaine, LSD, each for different reasons. Caffeine carriers make me thirsty, not good for singing. Cocaine is WAY out of my price range. LSD was fun 25 years ago but I tired of using a whole weekend that way and I can't begin to imagine being on it in a crowd, it was always a rural thing for me.

No one has mentioned outright that ubiquitous Rx self-medicator: codeine. Screws up my co-ordination pretty much like alcohol, intonation and tone are worse. So it's subject to the same limits. Once I get going with anything creative, back/leg pain disappears, emotional pain is forgotten.

Don't spend all this two cents in one place.

CH