Depressing it was, as well as visually stunning, but most critics would classify it as dark comedy, I think. Of course it's an anti-drug film extraordinaire, but the over the top camera work, the eye-popping rushes (Spun stole that), Burstyn's hallucinating refrigertor, the incredibly tragic endings that just overplayed any reasonable hope for the normal amount of 'luck', yeah it qualifies, imo .
Aronofsky's other classic indie, Pi, is more 'traditionally' darkcom.
If you found that depressing, check out Happiness. And the characters had no overriding addiction to balance the horrifying vulgarity of their lives.