Although it’s not clearly said in the novel, Charlie probably has several mental illnesses, including: Asperger's, PTSD (post-traumatic stress disorder), occasional depression, and perhaps drug(cannabis)-induced psychosis and/or schizophrenia. Before the end of the novel Charlie’s state of mental health deteriorates, because of his emerging PTSD (from the death of aunt Helen) and perhaps psychosis and/or schizophrenia. He is brought to a mental hospital, from which he finally recovers. Early in the book, it is mentioned that Charlie’s best friend Michael appeared to have suffered from depression and had killed himself (before the book). There are several more people in the book who appear to have depression and/or bipolar disorder.