In his memoir, David Sheff describes the incredibly vivid and harrowing images he found in his son's journals. There are breakdowns of the specific amount of each drug he has consumed, dark drawings of monsters with quotes about death, and many confessions about his addiction that he could never bear to say out loud at the time. While Nic's memoir, Tweak, was written based on his journal entries, the end credits of the movie reveal the truth behind Nic's onscreen journals.
Although Chalamet is deeply immersed in these drawings and confessions in the movie, the credits explain that the journal artwork was created by Nic's real brother, Jasper Sheff. With just a quick look at his Instagram account, we can see that Jasper is a seriously talented artist, so the fact that he was able to create these works of art for a movie about his brother's life proves how intimate and true to life the story is.
