To give some background to the creation of World of Darkness, the initial idea was put forth by Mark Rein-Hagen in a car trip with Stewart Wiek and Lisa Stevens.
While Rein-Hagen was on the road with Wieck and Stevens to GenCon 23
in 1990, he conceived of the game Vampire: The Masquerade which became
his main project for the next year, and was published by the new
company in 1991. Mage (1993) was based to a certain extent on a
game that Rein-Hagen had imagined back in 1989 as something like a
modern-day Ars Magica, although this was the first World of Darkness
game in which he was not explicitly involved.
— Wikipedia on Mark Rein-Hagen, cited from the book 'Designers and Dragons'
While not a perfectly rounded quote, I have found a reference dropped at a panel talk uploaded in 2009 where it's said, of one of the panelists and writers of Mage (not the same author as WoD) while writing the rules,
He spent most of the time in this haze...
This sentence could be interpreted in a variety of ways and imply the writer(s) of this particular work were under the effect of a drug, overwork or sleep deprivation (or otherwise intoxicated). However, as noted below by @JackLesnie, there is a culture of 'mystic oracle' which is promoted around the development of White Wolf games.
It should be noted that much of the early written work for World of Darkness was written by a collaborative team of freelancers in an office at White Wolf - but the implication of Mage being a fever dream seems to be common among the writers.
I am confident that with another week of trawling through panel discussions one might find more references to the phenomenon - though my research leads me to believe this is an inside joke, an issue of overwork, a reference to the flavour of Mage and a running aura of mystique.
I've attained a response to my rather invasive tweet to Stewart Wieck
Could you settle a dispute? Was Mage:Ascension "written in a perpetual state of intoxication" or is it a comment on mechanics?
Only if a constant diet of Indian food is intoxication. Lots of solo dinners in Decatur, GA pouring over notes and ideas.
Re: mechanics, Storyteller was a given, but the wonky bits I did with it (Spheres, Avatar, Arete, Paradox) is all on me.