Hunter used drugs, alcohol and all things illegal to an extreme; but if you read his writing you simultaneously see an author who is very sober-minded, who notices every detail and whom lives in every moment.
An example from the book:
'I didn't know Mr. Ackerman, but I remembered him coming aboard. He had the look of a man who had once been a tennis pro in Hong Kong, then gone on to bigger things. The gold Rolex, the white linen bush jacket, the Thai Bhat chain around his neck, the heavy leather briefcase with combination locks on every zipper...These were not signs of a man who would lock himself in the bathroom immediately after takeoff and stay inside for almost an hour.'
So Hunter was the ultimate paradox. A person who could kill a 12 pack of Miller High Life, a pint of Jack Daniels, hit a vial of LSD after swallowing a dozen pills in a 2 hour period on an airplane. But this same guy noticed everything and was really able to put that into his writing. I don't know how someone like this could exist, but obviously they do.