the dispensation he has to refuse himself
That codeine or maybe Percoset or maybe even Demerol wouldn’t be a relapse unless his heart of hearts that knew his motives thought it would be.
Context
The test at its cruelest: the permission comes from the program itself, from Pat, who tells him the narcotics wouldn't be a relapse unless his own heart knew otherwise — handing the whole judgment back to the man least able, in toxemic agony, to trust his own motives. So Gately interrogates his heart about codeine and gets no answer, left to white-knuckle a refusal that nobody but him is enforcing, against a pain everyone around him is urging him to medicate.