Metaphor?

Was this entire movie one big giant metaphor for drug addiction (specifically heroin)?
I got that vibe throughout the movie with all the needles, the pregnant women dying with a needle in her stomach (not that that's a regular place to shoot up, I'd imagine) and all the "feral" children because their parents are too high to raise them. The kids were licking the walls and the priest said every was "addicted" to it. It reminded me of the destitute and bleak nature, etc of Trainspotting, but with a horror element.