Corrected entry: There is absolutely no way that there would ever be a drug shortage in New York City. If that would ever happen then the DEA needs to pat themselves on the back until their hands break.
Corrected entry: When Harry is in the car with his friend driving to Florida, his friend hits his right arm and he winces, but it is later seen that it is his left arm that has the infection from shooting up. His friend didn't hit him that hard, so there would be no reason for Harry to wince unless it was intended to be the hurt arm.
Corrected entry: In the many scenes where Marion, Harry and Tyrone are injecting drugs, the pupils dilating is a mistake. The drug used in the movie is heroin, which constricts the pupils.
Corrected entry: A recurring feature is the shot of blood carrying the drug of choice to the the brain, a sigh of bliss and the dilation of the pupils. Sadly, heroin - the drug of choice of several main characters - causes the pupils to contract rather than dilate.