The hallucinogens produce visionary states, sort of, but morphine and its derivatives decrease awareness of inner processes, thoughts and feelings. They are pain killers; pure and simple. They are absolutely contraindicated for creative work, and I include in the lot alcohol, morphine, barbiturates, tranquilizers — the whole spectrum of sedative drugs.

Quoted in interview, The Paris Review (Fall 1965), in response to "The visions of drugs and the visions of art don't mix?"