I am at a loss to find a more honest depiction of how addiction is portrayed than in Aronofsky's work. Selby's book was already challenging in its portrayal of addiction, but the film shows addiction to be much worse: "By the end, he [Aronofsky] has made the movie bleaker than the original material. People may find it infuriating precisely because it's so intimidating, and it may leave you shaken. Be warned: it's a downer, and a knockout." Part of the reason why the film's ending is so sad and harsh to witness is because of its depiction of addiction.
In taking the most basic definition of addiction, one can see how the film accurately portrays it. Addiction can be seen as "the result of a powerful chain of molecular events that eventually compels an addict to get another fix, hit or drink." The film shows this with the quick cuts and sounds associated with injecting oneself with a drug or absorbing it through pills. Harry, Sara, Tyrone, and Marion all experience this sensation. The "powerful chain of molecular events" is shown whenever there are challenges being faced or when things are going well. For example, when Harry realizes that his mother is using drugs, that he is a reason for it and is helpless to stop it , he feels the impact of "a powerful chain of molecular events." He shoots up. When Marion needs inspiration for her work as a fashion designer, she is driven by "a powerful chain of molecular events." When Sara feels compelled to fit into "the red dress," this "powerful chain of molecular events" drives her to increase the dosage of the pills she takes to lose weight.
Addiction is shown to be not something of choice after a certain point. The characters are unable to stop their need for drugs. There is no external force that helps them moderate. In their forlorn predicament, the life of addiction is all that they know. Marion has to resort to prostitution in order to feed an addiction that is the only thing that cradles her and which she cradles at the end of the film. Tyrone is forced to live a life that will never come close to the warmth of his mother's lap. Instead, he lives alone in a Southern jail. Harry wishes to "score more" and loses an arm and his freedom in the process. Sara is consumed with "juice by Tappy" and is a shell of her former self as a result. Addiction is shown to be all consuming, which is an accurate read of how it can manifest itself if left unchecked and unabated.
There will be those who suggest that addiction is a choice and thus not shown accurately in the film. Yet, I think that if one accepts that drug use can easily facilitate the destructive tendencies of addiction, whereby one becomes so subsumed with drug use that all other perspective is lost, then the film shows this with stunning accuracy. It is for this reason that there is no redemption at the end of the film. There is no happiness evident. When Sara Goldfarb's friends are left weeping on a park bench for what has happened to her, we recognize their pain because that is what we have become upon the conclusion of the film. We can only weep for what we have seen, with the hope that such a predicament does not fall upon us or those we happen to love. It would be in this state of sadness where the film is accurate in its depiction of addiction.