Illicit opiat use during methadone maintenance.

The core hypothesis deduced from the Dole-Nyswander blockade formulation is that methadone is a sufficient but not necessary condition for abstinence from heroin. It is argued that this hypothesis has not been tested with scientifically adequate research. A research design is suggested. Since the Dole-Nyswander focus is at the physiological and metabolic level, it is argued that the blockade theory, pending, its scientific validation, should be supplemented by sociological, organizational, and economic theory.