Much of the book takes place in a substance abuse institution, which probably counts as a mental institution. There are other scenes in other types of psychiatric wards.
Arguable -- none of the characters specifically suffer from dysmorphia, but some characters are physically grotesque and their descriptions may be triggering.
In an early scene, a character is paralyzed by anxiety while waiting for a person to arrive, and the stream-of-consciousness style of the section may feel anxious to some readers.