Short story with anthropomorphic rats, deadly addictive drug, noir crime setting: Spoiler alert

Question

Seeking a pre-1980 (I believe) fantasy short story about crime and redemption. It’s written in the style of a gritty police procedural with the moral overtones of a classic detective story. The drug in question is overwhelmingly addictive with only one exposure and can corrupt even the most honorable people. The villain is a sentient, talking, rat crime boss/dealer, It’s never made clear how these rodents evolved or if they always have been present in this universe, I remember reading it a couple of times to try to figure it out, without success.

  The good cop who gets addicted overcomes the drug long enough to get the bad guy. The moral: This is what it means to be an honorable human versus a rat.

Answer 1

Perhaps "Rat" by James Patrick Kelly from 1986?

From the link:

Rat is a criminal, a drug runner and murderer. He is selfish, amoral, vindictive. Yet the reader gets caught up in his plight and begins to empathize with him for two reasons. One is that stories do that to us: putting even a despicable character in the role of protagonist and filtering events through that character's perceptions automatically slants our responses toward that character, even against our moral judgment. The way the story is set up seduces us into rooting for Rat to get home, to outwit his pursuers, to make his score. The other reason is that Rat is not a person but an animal, literally a rat, and everything he does is consistent with rat behavior: stealing, hiding, killing, surviving.