Man, that's a specific and brutal vibe. 'Last Exit' is such a raw, unflinching look at people on the edges. If you want more of that feeling of lives unraveling in harsh environments, I'd point you toward Hubert Selby Jr.'s other work, obviously. 'Requiem for a Dream' is just as devastating, maybe more so because it feels so relentless and internal.
Beyond Selby, Nelson Algren's 'The Man with the Golden Arm' digs into the grime of post-war Chicago with a similar sympathy for addicts and hustlers. The prose is a bit more lyrical, but the world is just as unforgiving. For a different angle, William T. Vollmann's 'The Rainbow Stories' or 'Whores for Gloria' offer a more sprawling, journalistic-yet-hallucinatory take on similar underworlds—skid row, prostitution, violence. It's not an easy read, but it’s memorable in that same 'I need a shower after this' way.
Honestly, a lot of modern crime fiction feels sanitized compared to this. You have to go back to that mid-20th century period or find authors specifically chasing that aesthetic of moral and physical decay.