non-overlapping stashes, the needle-dread, the Virus
The fact that Gately was devoted to Percocets and Bam-Bams and Fackelmann to Dilaudid allowed them a high level of trust with each other's stashes. Gately would do Blues, which had to be injected, only when no oral narcs were to be got and he was face to face with early Withdrawal. Gately feared and despised needles and was terrified of the Virus, which in those days was laying out needle-jockeys left and right.
Context
The using economy's fine print: two addicts can trust each other precisely because their appetites don't compete — oral man and needle man, each safe from the other's reach — and even inside the habit there's a floor Gately won't cross except when early Withdrawal forces it, the needle held off by dread of the Virus. The hierarchy of fears inside the addiction (needles below pills, the Virus below withdrawal) is its own map of how a user rations the ways he'll hurt himself.