The entire story of this film takes place in a world that is currently under the authority of evil, which seems to physically manifest in the entire atmosphere of the characters' surroundings. Dark alleys, tattered and abandoned buildings, no daylight, and plain scary-looking people all contribute to the intensity of the movie. (Actors portraying evil people wear colored contacts for a, well, evil appearance, for example.)
All fight/violent scenes are notably intense and frightening (see Violence & Gore), and the antagonists of the story also have a frightening nature about them.
The scene where the woman gets her body rid of drugs is not a pretty sight. Her arms distort and discolor, the injection sites open and black streams out of them, and we hear her crying out in pain. (See Alcohol/Drugs/Smoking.)