I feel that opiates - I include opium and all its derivatives, such as morphine, heroin, pantopon, etc. - are quite useless for any sort of creative work, useful though they may be for routine work. Much of the hard physical work in the Far East is done by opium addicts.
Burroughs Live: The Collected Interviews of William S. Burroughs, 1960-1997 (ed. Semiotext, 2001)