How does drug use/abuse transcend the actual usage to something more symbolic?

Duke and his attorney are heavy users of all kinds of drugs, but they demonstrate a preference for psychedelics such as LSD and mescaline. These drugs alter the user’s perception of reality, and the two men see these substances as enabling the ultimate escape from a troubling world. Throughout the text, Duke frequently describes his drug-induced delusions and hallucinations in detail. He seems to understand the line between reality and illusion, but he certainly believes that the content of his hallucinations can be significant and relevant to the world around him. Nevertheless, it is not always clear whether Duke’s perceptions at any given point are influenced by his drug use, which undermines his reliability as a narrator and gives the text a freewheeling, surreal quality.